Agent Identity Protocol (AIP) Specification

Version: v1alpha3
Status: Draft
Last Updated: 2026-02-19
Authors: Eduardo Arango ([email protected]),
James Cao ([email protected])

Abstract

The Agent Identity Protocol (AIP) defines a standard for identity, authentication, and policy-based authorization of AI agent tool calls. AIP enables runtime environments to enforce fine-grained access control over Model Context Protocol (MCP) tool invocations, providing a security boundary between AI agents and external resources. This specification defines:

The policy document schema (AgentPolicy)
Evaluation semantics for authorization decisions
Agent identity and session management
Server-side validation endpoints
Agent Authentication Token (AAT) and the identity layer (new in v1alpha3)
AIP Registry and Token Issuer (new in v1alpha3)
User binding and delegation (new in v1alpha3)
Error codes for denied requests
Audit log format for compliance

AIP is designed to be implementation-agnostic. Any MCP-compatible runtime (Cursor, Claude Desktop, VS Code, custom implementations) can implement this specification.

Introduction
Terminology
Policy Document Schema
Evaluation Semantics
Agent Identity
Server-Side Validation
Agent Authentication Token (AAT) (new in v1alpha3)
AIP Registry (new in v1alpha3)
Token Issuer (new in v1alpha3)
User Binding and Delegation (new in v1alpha3)
Error Codes
Audit Log Format
Conformance
Security Considerations
IANA Considerations

Appendices

Appendix A: Complete Schema Reference
Appendix B: Changelog
Appendix C: References
Appendix D: Future Extensions
Appendix E: Implementation Notes

1. Introduction

1.1 Motivation

AI agents operating through the Model Context Protocol (MCP) have access to powerful tools: file systems, databases, APIs, and cloud infrastructure. Without a policy layer, agents operate with unrestricted access to any tool the MCP server exposes. Today, agents are granted full permissions to API keys, secrets, and system resources, running as the user with no distinction between human and non-human actions. There is no universal way to distinguish an AI agent from a human actor. This creates systemic gaps:

No audit trail — agent actions are indistinguishable from human actions in logs
No revocation — once an agent has credentials, there is no standard way to revoke them
No authorization granularity — access is all-or-nothing at the API key level
Compliance blind spots — SOC 2, GDPR, HIPAA, and SOX requirements are unmet for agentic actions

AIP addresses these gaps through two interconnected layers:

Layer 1 — Identity: Establishes who the agent is via cryptographic identities, Agent Authentication Tokens, and a registry-based root of trust (formalized in v1alpha3)
Layer 2 — Enforcement: Decides what the agent is allowed to do via the AIP Proxy, policy engine, DLP scanning, and audit logging

The Agent Authentication Token (AAT) bridges these two layers — issued by Layer 1, enforced by Layer 2. AIP introduces:

Capability declaration: Explicit allowlists of permitted tools
Argument validation: Regex-based constraints on tool parameters
Human-in-the-loop: Interactive approval for sensitive operations
Audit trail: Immutable logging of all authorization decisions
Agent identity: Cryptographic binding of policies to agent sessions
Server-side validation: Optional HTTP endpoints for distributed policy enforcement
Agent Authentication Tokens: Signed tokens carrying agent identity, user delegation, and capabilities (new in v1alpha3)
Registry-based root of trust: Centralized agent registration with revocation (new in v1alpha3)
User binding: Cryptographic proof of which human authorized the agent (new in v1alpha3)

1.2 Goals

Interoperability: Any MCP runtime can implement AIP
Simplicity: YAML-based policies readable by security teams
Defense in depth: Multiple layers (method, tool, argument, identity, AAT)
Fail-closed: Unknown tools are denied by default
Zero-trust ready: Support for token-based identity verification
Agent-human distinction: Separate authentication for agents vs. users (new in v1alpha3)
Cryptographic delegation: Provable chain from user to agent to action (new in v1alpha3)

1.3 Non-Goals

The following are explicitly out of scope for this version of the specification:

Network egress control (see Appendix D: Future Extensions)
Subprocess sandboxing (implementation-defined)
Rate limiting algorithms (implementation-defined)
Policy expression languages beyond regex (CEL/Rego - see Appendix D)
Full OIDC/SPIFFE federation (see Appendix D); basic integration points are defined

1.4 Relationship to MCP

AIP is designed as a security layer for MCP. It intercepts tools/call requests and applies policy checks before forwarding to the MCP server.

┌─────────┐     ┌─────────────┐     ┌─────────────┐
│  Agent  │────▶│ AIP Policy  │────▶│ MCP Server  │
│         │◀────│   Engine    │◀────│             │
└─────────┘     └─────────────┘     └─────────────┘
                      │
                      ▼
              ┌─────────────┐
              │ AIP Server  │  (optional)
              │  Endpoint   │
              └─────────────┘

1.5 Relationship to MCP Authorization

MCP defines an optional OAuth 2.1-based authorization layer (MCP 2025-06-18 and later). AIP is complementary to MCP authorization:

Concern	MCP Authorization	AIP
Scope	Transport-level authentication	Tool-level authorization
What it protects	Access to MCP server	Access to specific tools
Token type	OAuth 2.1 access tokens	Agent Authentication Tokens (AAT)
Policy language	OAuth scopes	YAML policy documents
Identity model	User identity (OAuth)	Agent + user identity (AAT)

Implementations MAY use both MCP authorization (for server access) and AIP (for tool access) simultaneously.

1.6 Two-Layer Architecture (v1alpha3)

v1alpha3 formalizes the complete two-layer architecture:

         LAYER 1 -- IDENTITY                    LAYER 2 -- ENFORCEMENT
         (Who is this agent?)                  (What can it do?)

+-------------------+                       +-------------------+
|  AIP Registry     |  (Root of Trust)      |   AI Client       |
|  Registers Agents |                       | Cursor / Claude   |
|  Signs Certs      |                       +---------+---------+
+--------+----------+                                 | tool call + AAT
         | Issues Attestation                         v
         v                                  +---------------------------+
+-------------------+                       |       AIP Proxy           |
| Agent Identity    |                       |                           |
| Document (AID)    |                       | 1. Verify AAT signature   | <-- Registry
|  (Public Key)     |                       | 2. Check revocation list  |     (revocation)
+---------+---------+                       | 3. Validate user binding  |
          | Signs Token Requests            | 4. Check AAT capabilities |
          v                                 | 5. Evaluate local policy  |
+-------------------+                       | 6. DLP scan               |
|  Token Issuer     |                       | 7. Audit log              |
|  Validates ID     |      AAT             +---------+-----------------+
|  Binds User       | ---------------------->         | ALLOW / DENY
|  Issues AAT       |                                 v
+-------------------+                       +-------------------+
                                            |   Real Tool       |
                                            | Docker/Postgres   |
                                            | GitHub / etc.     |
                                            +-------------------+

Flow:

Agent registers with the AIP Registry, receiving a key pair and Agent Identity Document (AID)
When a user authorizes an agent, the Token Issuer validates the agent’s identity and issues an AAT encoding agent ID, user binding, and capabilities
On every tool call, the AIP Proxy verifies the AAT, checks the registry revocation list, evaluates policy, performs DLP scanning, and writes an audit log entry
A hijacked agent fails at Layer 2 — its AAT claims do not match the attempted action
A revoked agent fails at Layer 2 — the proxy checks the registry revocation list on every call
A legitimate agent passes through both layers with a full audit trail tied to its verified identity

2. Terminology

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.

Term	Definition
Agent	An AI system that invokes MCP tools on behalf of a user
Agent Identity Document (AID)	JSON structure defining an agent’s cryptographic identity (new)
Agent Authentication Token (AAT)	A signed token proving agent identity, user delegation, and capabilities at runtime (new)
AIP Registry	Central directory of registered agents and their public keys (new)
Token Issuer	Service that validates agent identity and issues AATs (new)
Policy	A document specifying authorization rules (AgentPolicy)
Tool	An MCP tool exposed by an MCP server
Decision	The result of policy evaluation: ALLOW, BLOCK, or ASK
Violation	A policy rule was triggered (may or may not block)
Session	A bounded period of agent activity with consistent identity
Identity Token	A cryptographic token binding policy to session (v1alpha2; superseded by AAT for cross-service use)
Policy Hash	SHA-256 hash of the canonical policy document
User Binding	Cryptographic proof linking an agent’s actions to an authorizing user (new)
Capability	A declared permission encoded in an AAT (e.g., tool access, resource scope) (new)
Delegation Chain	The provable path from user authorization through agent to action (new)
Revocation List	Registry-maintained list of revoked agents, AATs, and sessions (new)

3. Policy Document Schema

3.1 Document Structure

An AIP policy document is a YAML file with the following top-level structure:

apiVersion: aip.io/v1alpha3
kind: AgentPolicy
metadata:
  name: <string>
  version: <string>           # OPTIONAL
  owner: <string>             # OPTIONAL
  signature: <string>         # OPTIONAL
spec:
  mode: <string>              # OPTIONAL, default: "enforce"
  allowed_tools: [<string>]   # OPTIONAL
  allowed_methods: [<string>] # OPTIONAL
  denied_methods: [<string>]  # OPTIONAL
  tool_rules: [<ToolRule>]    # OPTIONAL
  protected_paths: [<string>] # OPTIONAL
  strict_args_default: <bool> # OPTIONAL, default: false
  dlp: <DLPConfig>            # OPTIONAL
  identity: <IdentityConfig>  # OPTIONAL
  server: <ServerConfig>      # OPTIONAL
  registry: <RegistryConfig>  # OPTIONAL (v1alpha3)
  aat: <AATConfig>            # OPTIONAL (v1alpha3)

3.2 Required Fields

Field	Type	Description
`apiVersion`	string	MUST be `aip.io/v1alpha3`
`kind`	string	MUST be `AgentPolicy`
`metadata.name`	string	Unique identifier for this policy

3.3 Metadata

metadata:
  name: <string>        # REQUIRED - Policy identifier
  version: <string>     # OPTIONAL - Semantic version (e.g., "1.0.0")
  owner: <string>       # OPTIONAL - Contact email
  signature: <string>   # OPTIONAL - Policy signature

3.3.1 Policy Signature

The signature field provides cryptographic integrity verification for the policy document. Format: <algorithm>:<base64-encoded-signature> Supported algorithms:

ed25519 - Ed25519 signature (RECOMMENDED)

Example:

metadata:
  name: production-agent
  signature: "ed25519:YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXo..."

When present, implementations MUST verify the signature before applying the policy. Signature verification failure MUST result in policy rejection. The signature is computed over the canonical form of the policy document (see Section 5.2.1).

3.4 Spec Fields

[Sections 3.4.1 through 3.4.6 remain unchanged from v1alpha2]

3.4.1 mode

Controls enforcement behavior.

Value	Behavior
`enforce`	Violations are blocked (default)
`monitor`	Violations are logged but allowed

Implementations MUST support both modes.

3.4.2 allowed_tools

A list of tool names that the agent MAY invoke.

allowed_tools:
  - github_get_repo
  - read_file
  - list_directory

Tool names are subject to normalization (see Section 4.1).

3.4.3 allowed_methods

A list of JSON-RPC methods that are permitted. If not specified, implementations MUST use the default safe list:

# Default allowed methods (when not specified)
allowed_methods:
  - initialize
  - initialized
  - ping
  - tools/call
  - tools/list
  - completion/complete
  - notifications/initialized
  - notifications/progress
  - notifications/message
  - notifications/resources/updated
  - notifications/resources/list_changed
  - notifications/tools/list_changed
  - notifications/prompts/list_changed
  - cancelled

The wildcard * MAY be used to allow all methods.

3.4.4 denied_methods

A list of JSON-RPC methods that are explicitly denied. Denied methods take precedence over allowed methods.

denied_methods:
  - resources/read
  - resources/write

3.4.5 protected_paths

A list of file paths that tools MUST NOT access. Any tool argument containing a protected path MUST be blocked.

protected_paths:
  - ~/.ssh
  - ~/.aws/credentials
  - .env

Implementations MUST:

Expand ~ to the user’s home directory
Automatically protect the policy file itself

3.4.6 strict_args_default

When true, tool rules reject any arguments not explicitly declared in allow_args. Default: false

3.5 Tool Rules

Tool rules provide fine-grained control over specific tools.

tool_rules:
  - tool: <string>              # REQUIRED - Tool name
    action: <string>            # OPTIONAL - allow|block|ask (default: allow)
    rate_limit: <string>        # OPTIONAL - e.g., "10/minute"
    strict_args: <bool>         # OPTIONAL - Override strict_args_default
    schema_hash: <string>       # OPTIONAL - Tool schema integrity
    allow_args:                 # OPTIONAL
      <arg_name>: <regex>

3.5.1 Actions

Action	Behavior
`allow`	Permit (subject to argument validation)
`block`	Deny unconditionally
`ask`	Require interactive user approval

3.5.2 Rate Limiting

Format: <count>/<period>

Period	Aliases
`second`	`sec`, `s`
`minute`	`min`, `m`
`hour`	`hr`, `h`

Example: "10/minute", "100/hour", "5/second" Rate limiting algorithm is implementation-defined (token bucket, sliding window, etc.).

3.5.3 Argument Validation

The allow_args field maps argument names to regex patterns.

allow_args:
  url: "^https://github\\.com/.*"
  query: "^SELECT\\s+.*"

Implementations MUST:

Use a regex engine with linear-time guarantees (RE2 or equivalent)
Match against the string representation of the argument value
Treat missing constrained arguments as a violation

3.5.4 Tool Schema Hashing

The schema_hash field provides cryptographic verification of tool definitions to prevent tool poisoning attacks. Format: <algorithm>:<hex-digest> Supported algorithms:

sha256 (RECOMMENDED)
sha384
sha512

Hash computation:

TOOL_SCHEMA_HASH(tool):
  schema = {
    "name": tool.name,
    "description": tool.description,
    "inputSchema": tool.inputSchema
  }
  canonical = JSON_CANONICALIZE(schema)  # RFC 8785
  hash = SHA256(canonical)
  RETURN "sha256:" + hex_encode(hash)

Condition	Behavior
`schema_hash` absent	No schema verification (backward compatible)
Hash matches	Tool allowed (proceed to argument validation)
Hash mismatch	Tool BLOCKED with error -32013
Tool not found	Tool BLOCKED with error -32001

3.6 DLP Configuration

[Section 3.6 remains unchanged from v1alpha2] Data Loss Prevention (DLP) scans for sensitive data in requests and responses.

dlp:
  enabled: <bool>             # OPTIONAL, default: true when dlp block present
  scan_requests: <bool>       # OPTIONAL, default: false
  scan_responses: <bool>      # OPTIONAL, default: true
  detect_encoding: <bool>     # OPTIONAL, default: false
  filter_stderr: <bool>       # OPTIONAL, default: false
  max_scan_size: <string>     # OPTIONAL, default: "1MB"
  on_request_match: <string>  # OPTIONAL, default: "block"
  on_redaction_failure: <string>    # OPTIONAL, default: "block"
  log_original_on_failure: <bool>   # OPTIONAL, default: false
  patterns:
    - name: <string>          # REQUIRED - Rule identifier
      regex: <string>         # REQUIRED - Detection pattern
      scope: <string>         # OPTIONAL, default: "all" (request|response|all)

When a pattern matches, the matched content MUST be replaced with:

[REDACTED:<name>]

3.7 Identity Configuration

[Section 3.7 remains unchanged from v1alpha2] The identity section configures agent identity and token management.

spec:
  identity:
    enabled: <bool>           # OPTIONAL, default: false
    token_ttl: <duration>     # OPTIONAL, default: "5m"
    rotation_interval: <duration>  # OPTIONAL, default: "4m"
    require_token: <bool>     # OPTIONAL, default: false
    session_binding: <string> # OPTIONAL, default: "process"
    nonce_window: <duration>  # OPTIONAL, default: equals token_ttl
    policy_transition_grace: <duration>  # OPTIONAL, default: "0s"
    audience: <string>        # OPTIONAL, default: policy metadata.name
    nonce_storage: <NonceStorageConfig>  # OPTIONAL
    keys: <KeyConfig>         # OPTIONAL

3.8 Server Configuration

[Section 3.8 remains unchanged from v1alpha2]

spec:
  server:
    enabled: <bool>           # OPTIONAL, default: false
    listen: <string>          # OPTIONAL, default: "127.0.0.1:9443"
    failover_mode: <string>   # OPTIONAL, default: "fail_closed"
    timeout: <duration>       # OPTIONAL, default: "5s"
    tls:
      cert: <string>
      key: <string>
    endpoints:
      validate: <string>      # default: "/v1/validate"
      revoke: <string>        # default: "/v1/revoke"
      jwks: <string>          # default: "/v1/jwks"
      health: <string>        # default: "/health"
      metrics: <string>       # default: "/metrics"

3.9 Registry Configuration (v1alpha3)

The registry section configures how the AIP Proxy connects to the AIP Registry for agent verification and revocation checks.

spec:
  registry:
    enabled: <bool>                 # OPTIONAL, default: false
    endpoint: <string>              # REQUIRED if enabled - Registry URL
    tls:                            # OPTIONAL
      ca_cert: <string>            # Path to CA certificate for registry
      client_cert: <string>        # Path to client certificate (mTLS)
      client_key: <string>         # Path to client key (mTLS)
    cache:                          # OPTIONAL
      enabled: <bool>              # default: true
      ttl: <duration>              # default: "5m"
      max_entries: <int>           # default: 10000
    revocation:                     # OPTIONAL
      check_interval: <duration>   # default: "30s"
      mode: <string>               # "online" | "cached" | "crl"
      crl_path: <string>           # Path to local CRL file (if mode=crl)
    auth:                           # OPTIONAL
      type: <string>               # "bearer" | "mtls" | "api_key"
      token: <string>              # Bearer token for registry access
      api_key: <string>            # API key for registry access

3.9.1 enabled

When true, the AIP Proxy connects to an AIP Registry for agent identity verification and revocation checking. Default: false When registry.enabled: true, the proxy MUST verify AATs against the registry’s known agent keys before applying local policy.

3.9.2 endpoint

The URL of the AIP Registry. Format: https://<host>:<port> Example:

registry:
  enabled: true
  endpoint: "https://registry.aip.example.com"

3.9.3 Revocation Modes

Mode	Description	Latency	Freshness
`online`	Check registry on every AAT validation	High	Real-time
`cached`	Cache revocation list, refresh periodically (default)	Low	Eventual
`crl`	Load Certificate Revocation List from local file	Lowest	Manual

online (highest security):

registry:
  revocation:
    mode: "online"

Every AAT validation queries the registry
Highest security, highest latency
Requires reliable network connectivity

cached (RECOMMENDED for production):

registry:
  revocation:
    mode: "cached"
    check_interval: "30s"

Background refresh of revocation list
Trades freshness for performance
Revocations take effect within check_interval

crl (air-gapped or offline environments):

registry:
  revocation:
    mode: "crl"
    crl_path: "/etc/aip/revocation.crl"
    check_interval: "5m"  # Re-read CRL file

CRL file updated by external process
No network dependency
Manual revocation propagation

3.9.4 Cache Configuration

registry:
  cache:
    enabled: true
    ttl: "5m"
    max_entries: 10000

Field	Type	Default	Description
`enabled`	bool	`true`	Cache agent public keys and revocation status
`ttl`	duration	`"5m"`	Cache entry time-to-live
`max_entries`	int	`10000`	Maximum cached entries (LRU eviction)

3.10 AAT Configuration (v1alpha3)

The aat section configures how the AIP Proxy validates and uses Agent Authentication Tokens.

spec:
  aat:
    enabled: <bool>               # OPTIONAL, default: false
    require: <bool>               # OPTIONAL, default: false
    validation:                   # OPTIONAL
      verify_signature: <bool>    # default: true
      verify_user_binding: <bool> # default: true
      verify_capabilities: <bool> # default: true
      max_token_age: <duration>   # default: "1h"
      clock_skew: <duration>      # default: "30s"
    capabilities_mode: <string>   # OPTIONAL, default: "intersect"
    trusted_issuers: [<string>]   # OPTIONAL - List of trusted Token Issuer IDs
    header_name: <string>         # OPTIONAL, default: "X-AIP-AAT"

3.10.1 enabled

When true, the proxy accepts and validates AATs on incoming requests. Default: false

3.10.2 require

When true, all tool calls MUST include a valid AAT. Calls without AATs are rejected with error code -32015. Default: false This enables gradual rollout: start with require: false to validate AATs when present without blocking requests that lack them.

3.10.3 capabilities_mode

Determines how AAT capabilities interact with local policy.

Value	Behavior
`intersect`	Tool must be allowed by BOTH AAT capabilities and local policy (default)
`aat_only`	AAT capabilities replace local `allowed_tools`
`policy_only`	Local policy only; AAT used for identity/audit only

intersect (RECOMMENDED):

aat:
  capabilities_mode: "intersect"

Most restrictive: requires both AAT and local policy to allow the tool
Defense in depth: neither AAT compromise nor policy compromise alone grants access

aat_only (registry-managed environments):

aat:
  capabilities_mode: "aat_only"

Centralized capability management via Token Issuer
Local policy still enforces argument validation, DLP, and rate limiting
allowed_tools in local policy is IGNORED

policy_only (audit-focused deployments):

aat:
  capabilities_mode: "policy_only"

AAT used only for identity verification and audit trail enrichment
Local policy controls all authorization decisions
Simplest migration path from v1alpha2

3.10.4 trusted_issuers

A list of Token Issuer identifiers whose AATs are accepted by this proxy.

aat:
  trusted_issuers:
    - "https://issuer.aip.example.com"
    - "https://issuer.aip.corp.internal"

When specified, the proxy MUST reject AATs from issuers not in this list. When not specified, the proxy accepts AATs from any issuer whose public key can be verified via the registry.

3.10.5 header_name

The HTTP header or JSON-RPC extension field used to transmit AATs. Default: "X-AIP-AAT" For JSON-RPC transport (stdio), the AAT is included in the request params:

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "read_file",
    "arguments": {"path": "/etc/hosts"},
    "_aip_aat": "<base64url-encoded-aat>"
  }
}

For HTTP transport, the AAT is sent as a header:

POST /v1/validate HTTP/1.1
X-AIP-AAT: <base64url-encoded-aat>

The _aip_aat parameter is reserved by this specification and MUST NOT be forwarded to the MCP server.

4. Evaluation Semantics

4.1 Name Normalization

Tool names and method names MUST be normalized before comparison using the following algorithm:

NORMALIZE(input):
Apply NFKC Unicode normalization
Convert to lowercase
Trim leading/trailing whitespace
Remove non-printable and control characters
Return result

4.2 Method-Level Authorization

Method authorization is the FIRST line of defense, evaluated BEFORE tool-level checks.

IS_METHOD_ALLOWED(method):
  normalized = NORMALIZE(method)

  IF normalized IN denied_methods:
    RETURN DENY

  IF "*" IN allowed_methods:
    RETURN ALLOW

  IF normalized IN allowed_methods:
    RETURN ALLOW

  RETURN DENY

4.3 Tool-Level Authorization

Tool authorization applies to tools/call requests.

IS_TOOL_ALLOWED(tool_name, arguments, identity_token, aat):
  normalized = NORMALIZE(tool_name)

  # Step 0: Verify identity token (if configured)
  IF identity.require_token:
    IF identity_token IS EMPTY OR NOT valid_token(identity_token):
      RETURN TOKEN_REQUIRED

  # Step 0b: Verify AAT (v1alpha3)
  IF aat.require:
    IF aat IS EMPTY:
      RETURN AAT_REQUIRED
    IF NOT valid_aat(aat):
      RETURN AAT_INVALID
  ELSE IF aat IS PRESENT:
    # Validate opportunistically even when not required
    IF NOT valid_aat(aat):
      LOG_WARNING("Invalid AAT presented but not required")

  # Step 0c: Check AAT capabilities (v1alpha3)
  IF aat IS PRESENT AND aat IS VALID:
    IF aat.capabilities_mode == "intersect":
      IF normalized NOT IN aat.capabilities:
        RETURN AAT_CAPABILITY_DENIED
    ELSE IF aat.capabilities_mode == "aat_only":
      IF normalized NOT IN aat.capabilities:
        RETURN AAT_CAPABILITY_DENIED
      SKIP local allowed_tools check (Step 4)

  # Step 1: Check rate limiting
  IF rate_limiter_exceeded(normalized):
    RETURN RATE_LIMITED

  # Step 2: Check protected paths
  IF arguments_contain_protected_path(arguments):
    RETURN PROTECTED_PATH

  # Step 3: Check tool rules
  rule = find_rule(normalized)
  IF rule EXISTS:
    IF rule.action == "block":
      RETURN BLOCK
    IF rule.action == "ask":
      IF validate_arguments(rule, arguments):
        RETURN ASK
      ELSE:
        RETURN BLOCK

  # Step 4: Check allowed_tools list (skipped if aat_only mode)
  IF aat.capabilities_mode != "aat_only":
    IF normalized NOT IN allowed_tools:
      RETURN BLOCK

  # Step 5: Validate arguments (if rule exists)
  IF rule EXISTS AND rule.allow_args NOT EMPTY:
    IF NOT validate_arguments(rule, arguments):
      RETURN BLOCK

  # Step 6: Strict args check
  IF strict_args_enabled(rule):
    IF arguments has undeclared keys:
      RETURN BLOCK

  RETURN ALLOW

4.4 Decision Outcomes

Decision	Mode=enforce	Mode=monitor
ALLOW	Forward request	Forward request
BLOCK	Return error	Forward request, log violation
ASK	Prompt user	Prompt user
RATE_LIMITED	Return error	Return error (always enforced)
PROTECTED_PATH	Return error	Return error (always enforced)
TOKEN_REQUIRED	Return error	Return error (always enforced)
TOKEN_INVALID	Return error	Return error (always enforced)
AAT_REQUIRED	Return error	Return error (always enforced) (new)
AAT_INVALID	Return error	Return error (always enforced) (new)
AAT_CAPABILITY_DENIED	Return error	Forward request, log violation (new)

4.5 Argument Validation

VALIDATE_ARGUMENTS(rule, arguments):
  FOR EACH (arg_name, pattern) IN rule.allow_args:
    IF arg_name NOT IN arguments:
      RETURN FALSE  # Required argument missing

    value = STRING(arguments[arg_name])
    IF NOT REGEX_MATCH(pattern, value):
      RETURN FALSE

  RETURN TRUE

The STRING() function converts values to string representation:

String -> as-is
Number -> decimal representation
Boolean -> “true” or “false”
Null -> empty string
Array/Object -> JSON serialization

5. Agent Identity

[Section 5 remains unchanged from v1alpha2] This section defines the local agent identity model introduced in v1alpha2. In v1alpha3, local identity tokens and AATs serve complementary roles: identity tokens bind the proxy session, while AATs carry cross-service agent identity.

5.1 Overview

Agent identity provides:

Session binding: Cryptographic proof that requests belong to the same session
Policy integrity: Verification that the policy hasn’t changed mid-session
Replay prevention: Nonces prevent token reuse across sessions
Audit correlation: Session IDs link related audit events

5.2 Policy Hash

5.2.1 Canonical Form

CANONICALIZE(policy):
Remove metadata.signature field (if present)
Serialize to JSON using RFC 8785 (JSON Canonicalization Scheme)
Return UTF-8 encoded bytes

5.2.2 Hash Computation

POLICY_HASH(policy):
  canonical = CANONICALIZE(policy)
  hash = SHA-256(canonical)
  RETURN hex_encode(hash)

5.3 Identity Token Structure

[Remains unchanged from v1alpha2]

5.4 Token Lifecycle

[Remains unchanged from v1alpha2]

5.5 Session Management

[Remains unchanged from v1alpha2]

5.6 Token and Session Revocation

[Remains unchanged from v1alpha2]

5.7 Compatibility with Agentic JWT

[Remains unchanged from v1alpha2]

5.8 Key Management

[Remains unchanged from v1alpha2]

6. Server-Side Validation

[Section 6 remains unchanged from v1alpha2, with the addition of AAT-aware endpoints]

6.1 Overview

The AIP server provides:

Remote validation: Validate tool calls from external systems
Health checks: Integration with load balancers and orchestrators
Metrics: Prometheus-compatible metrics export
AAT validation: Verify Agent Authentication Tokens (new in v1alpha3)

6.2 Validation Endpoint

6.2.1 Request Format

POST /v1/validate HTTP/1.1
Host: aip-server:9443
Content-Type: application/json
Authorization: Bearer <identity-token>
X-AIP-AAT: <agent-authentication-token>

{
  "tool": "<tool-name>",
  "arguments": { ... }
}

When both an identity token and an AAT are present, the proxy MUST validate both. The identity token authenticates the proxy session; the AAT authenticates the agent.

6.2.2 Response Format

HTTP/1.1 200 OK
Content-Type: application/json

{
  "decision": "allow|block|ask",
  "reason": "<human-readable-reason>",
  "violations": [
    {
      "type": "<violation-type>",
      "field": "<field-name>",
      "message": "<description>"
    }
  ],
  "token_status": {
    "valid": true,
    "expires_in": 240
  },
  "aat_status": {
    "valid": true,
    "agent_id": "<agent-id>",
    "user_id": "<user-id>",
    "capabilities_checked": true,
    "issuer": "<issuer-id>"
  }
}

6.3 Health Endpoint

[Remains unchanged from v1alpha2]

6.4 Metrics Endpoint

Updated metrics (v1alpha3 additions):

Metric	Type	Description
`aip_requests_total`	counter	Total validation requests
`aip_decisions_total`	counter	Decisions by type (allow/block/ask)
`aip_violations_total`	counter	Policy violations by type
`aip_token_validations_total`	counter	Identity token validations (valid/invalid)
`aip_aat_validations_total`	counter	AAT validations (valid/invalid/expired/revoked) (new)
`aip_registry_checks_total`	counter	Registry revocation checks (new)
`aip_registry_latency_seconds`	histogram	Registry check latency (new)
`aip_revocations_total`	counter	Revocation events by type
`aip_active_sessions`	gauge	Currently active sessions
`aip_active_agents`	gauge	Currently active agents (by AAT) (new)
`aip_request_duration_seconds`	histogram	Request latency
`aip_policy_hash`	gauge	Current policy hash (as label)

6.5 Revocation Endpoint

[Remains unchanged from v1alpha2]

6.6 Authentication

[Remains unchanged from v1alpha2]

7. Agent Authentication Token (AAT) (v1alpha3)

This section defines the Agent Authentication Token — the core credential bridging Layer 1 (Identity) and Layer 2 (Enforcement).

7.1 Overview

The AAT carries signed claims about an agent:

Who issued its identity — the Token Issuer
Which user it is acting on behalf of — user binding
What capabilities it declared — tools and resource scopes
When it was issued and when it expires — temporal bounds

The AAT enables:

Per-agent identity: Every agent has a distinct cryptographic identity, separate from the user
User delegation: Actions are provably linked to the authorizing human
Capability-based authorization: AAT capabilities can drive policy decisions
Cross-service portability: AATs are verifiable by any party with access to the issuer’s public key

7.2 AAT Structure

An AAT is a signed JWT (RFC 7519) with the following claims:

{
  "aat_version": "aip/v1alpha3",
  "iss": "<token-issuer-id>",
  "sub": "<agent-id>",
  "aud": "<target-service-or-proxy>",
  "iat": 1708300800,
  "exp": 1708304400,
  "nbf": 1708300800,
  "jti": "<unique-token-id>",

  "agent": {
    "id": "<agent-id>",
    "name": "<human-readable-agent-name>",
    "public_key_thumbprint": "<sha256-of-agent-public-key>",
    "aid_hash": "<sha256-of-agent-identity-document>"
  },

  "user_binding": {
    "user_id": "<user-identifier>",
    "auth_method": "<how-user-authenticated>",
    "auth_time": 1708300000,
    "delegation_scope": "<scope-of-delegation>"
  },

  "capabilities": {
    "tools": ["<tool-name>", ...],
    "resource_scopes": ["<scope>", ...],
    "max_calls_per_session": <int>,
    "allowed_servers": ["<mcp-server-id>", ...]
  },

  "context": {
    "session_id": "<uuid>",
    "policy_hash": "<64-char-hex>",
    "registry_id": "<registry-identifier>"
  }
}

7.3 AAT Claims

7.3.1 Standard JWT Claims

Claim	Type	Required	Description
`aat_version`	string	Yes	MUST be `aip/v1alpha3`
`iss`	string	Yes	Token Issuer identifier (URI)
`sub`	string	Yes	Agent identifier (from AID)
`aud`	string/array	Yes	Intended recipient(s) — proxy or MCP server
`iat`	number	Yes	Issued-at time (Unix timestamp)
`exp`	number	Yes	Expiration time (Unix timestamp)
`nbf`	number	No	Not-before time (Unix timestamp)
`jti`	string	Yes	Unique token identifier (UUID v4)

7.3.2 Agent Claims

The agent object identifies the AI agent:

Field	Type	Required	Description
`id`	string	Yes	Unique agent identifier (from registry)
`name`	string	No	Human-readable name (e.g., “Cursor IDE Agent”)
`public_key_thumbprint`	string	Yes	SHA-256 of agent’s public key (JWK Thumbprint, RFC 7638)
`aid_hash`	string	No	SHA-256 of the Agent Identity Document

The public_key_thumbprint allows the proxy to verify that the AAT was issued for the specific agent key pair, preventing AAT theft across agents.

7.3.3 User Binding Claims

The user_binding object links the agent’s actions to the authorizing human:

Field	Type	Required	Description
`user_id`	string	Yes	User identifier (email, OIDC sub, or opaque ID)
`auth_method`	string	Yes	How the user authenticated (see below)
`auth_time`	number	Yes	When the user authenticated (Unix timestamp)
`delegation_scope`	string	No	Scope of delegation granted to the agent

auth_method values:

Value	Description
`oidc`	OpenID Connect authentication
`oauth2`	OAuth 2.0 authorization code flow
`api_key`	API key associated with a user
`local`	Local system user (process owner)
`saml`	SAML assertion
`attestation`	Hardware or platform attestation

delegation_scope values:

Value	Description
`full`	Agent can perform any action the user could (NOT RECOMMENDED)
`tools`	Agent can use specific tools listed in `capabilities.tools`
`read_only`	Agent can only use read operations
`session`	Delegation valid for this session only
`custom:<scope>`	Implementation-defined scope

7.3.4 Capabilities Claims

The capabilities object declares what the agent is authorized to do:

Field	Type	Required	Description
`tools`	[]string	No	List of tool names the agent may invoke
`resource_scopes`	[]string	No	Resource access scopes (e.g., `repo:read`, `db:write`)
`max_calls_per_session`	int	No	Maximum tool calls allowed in this session
`allowed_servers`	[]string	No	MCP server identifiers this AAT is valid for

Capability resolution (how AAT capabilities interact with local policy):

RESOLVE_CAPABILITIES(aat, local_policy, mode):
  IF mode == "intersect":
    RETURN INTERSECTION(aat.capabilities.tools, local_policy.allowed_tools)

  IF mode == "aat_only":
    RETURN aat.capabilities.tools

  IF mode == "policy_only":
    RETURN local_policy.allowed_tools

resource_scopes: Resource scopes follow a <resource>:<action> format:

{
  "resource_scopes": [
    "repo:read",
    "repo:write",
    "db:read",
    "file:/home/user/**:read",
    "api:github.com:*"
  ]
}

Resource scopes are advisory in v1alpha3. Future versions MAY make them enforceable.

7.3.5 Context Claims

The context object provides operational context:

Field	Type	Required	Description
`session_id`	string	Yes	Session UUID (matches identity token session)
`policy_hash`	string	No	SHA-256 hash of the policy the issuer approved
`registry_id`	string	No	Registry that holds the agent’s registration

7.4 AAT Signing

AATs MUST be signed using one of the following algorithms (in order of preference):

Algorithm	Key Type	Recommendation
`ES256`	ECDSA P-256	Default, RECOMMENDED
`ES384`	ECDSA P-384	High-security environments
`EdDSA`	Ed25519	Performance-critical
`RS256`	RSA 2048+	Legacy compatibility

AATs MUST NOT use symmetric algorithms (HS256) as they require shared secrets. JWT Header:

{
  "alg": "ES256",
  "typ": "aat+jwt",
  "kid": "<key-id-of-issuer-signing-key>"
}

The kid MUST reference a key in the Token Issuer’s JWKS endpoint or the AIP Registry’s key store.

7.5 AAT Lifecycle

┌──────────────┐
│  User Grants  │
│  Delegation   │
└──────┬───────┘
       │
       ▼
┌──────────────┐     ┌──────────────┐
│ Token Issuer │────▶│   Active     │
│  Issues AAT  │     │     AAT      │
└──────────────┘     └──────┬───────┘
                            │
       ┌────────────────────┼────────────────────┐
       │                    │                    │
       ▼                    ▼                    ▼
┌──────────────┐     ┌──────────────┐     ┌──────────────┐
│   Refresh    │     │   Expired    │     │   Revoked    │
│   (new AAT)  │     │   (reject)   │     │  (by registry│
└──────────────┘     └──────────────┘     │  or issuer)  │
                                          └──────────────┘

7.5.1 AAT Issuance

Agent authenticates to Token Issuer using its private key (proof of possession)
User authorization is verified (OAuth flow, API key lookup, or local attestation)
Token Issuer retrieves agent registration from AIP Registry
Token Issuer constructs AAT with agent identity, user binding, and capabilities
Token Issuer signs AAT with its private key
AAT returned to agent

7.5.2 AAT Refresh

AATs SHOULD be refreshed before expiry. The refresh flow:

Agent presents current AAT and proof of possession (signed challenge)
Token Issuer verifies current AAT is valid (not expired, not revoked)
Token Issuer checks registry for revocation
New AAT issued with same session_id, fresh jti, updated exp

Constraints:

Refreshed AAT MUST preserve the session_id
Refreshed AAT MUST have a new jti
Refreshed AAT MAY have different capabilities (if policy changed)
Refresh MUST fail if the agent or session is revoked

7.5.3 AAT Validation

The AIP Proxy MUST validate AATs using the following algorithm:

VALIDATE_AAT(aat):
  # Step 1: Parse and verify JWT structure
  IF NOT valid_jwt_structure(aat):
    RETURN (INVALID, "malformed_aat")

  # Step 2: Verify version
  IF aat.aat_version != "aip/v1alpha3":
    RETURN (INVALID, "unsupported_version")

  # Step 3: Verify issuer
  IF trusted_issuers IS CONFIGURED:
    IF aat.iss NOT IN trusted_issuers:
      RETURN (INVALID, "untrusted_issuer")

  # Step 4: Verify signature
  issuer_key = GET_ISSUER_PUBLIC_KEY(aat.iss, aat.header.kid)
  IF issuer_key IS NULL:
    RETURN (INVALID, "unknown_signing_key")
  IF NOT verify_signature(aat, issuer_key):
    RETURN (INVALID, "signature_invalid")

  # Step 5: Check temporal validity
  now = current_time()
  IF now < aat.nbf - clock_skew:
    RETURN (INVALID, "not_yet_valid")
  IF now > aat.exp + clock_skew:
    RETURN (INVALID, "aat_expired")

  # Step 6: Check audience
  IF aat.aud does not match expected_audience:
    RETURN (INVALID, "audience_mismatch")

  # Step 7: Check revocation (via registry)
  IF registry.enabled:
    revocation_status = CHECK_REGISTRY_REVOCATION(aat)
    IF revocation_status == REVOKED:
      RETURN (INVALID, "aat_revoked")

  # Step 8: Verify agent identity
  IF registry.enabled:
    agent_record = GET_AGENT_FROM_REGISTRY(aat.agent.id)
    IF agent_record IS NULL:
      RETURN (INVALID, "unknown_agent")
    IF agent_record.public_key_thumbprint != aat.agent.public_key_thumbprint:
      RETURN (INVALID, "agent_key_mismatch")
    IF agent_record.status != "active":
      RETURN (INVALID, "agent_inactive")

  # Step 9: Verify JTI uniqueness (replay prevention)
  IF NOT ATOMIC_CHECK_AND_RECORD_JTI(aat.jti):
    RETURN (INVALID, "replay_detected")

  RETURN (VALID, nil)

7.6 AAT Transport

7.6.1 JSON-RPC (stdio) Transport

For MCP connections over stdio, the AAT is included in the tools/call params as a reserved field:

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "read_file",
    "arguments": {"path": "/etc/hosts"},
    "_aip_aat": "eyJhbGciOiJFUzI1NiIsInR5cCI6ImFhdCtqd3QifQ..."
  }
}

The _aip_aat field:

MUST be stripped by the AIP Proxy before forwarding to the MCP server
MUST NOT be logged in audit trails (log jti instead)
Is OPTIONAL when aat.require: false

7.6.2 HTTP Transport

For HTTP-based MCP connections, the AAT is sent as a header:

POST /mcp HTTP/1.1
X-AIP-AAT: eyJhbGciOiJFUzI1NiIsInR5cCI6ImFhdCtqd3QifQ...
Content-Type: application/json

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "read_file",
    "arguments": {"path": "/etc/hosts"}
  }
}

8. AIP Registry (v1alpha3)

The AIP Registry is the root of trust for agent identities.

8.1 Overview

The AIP Registry provides:

Agent registration: Agents register their public keys and metadata
Key attestation: Registry signs agent certificates (Agent Identity Documents)
Revocation: Registry maintains lists of revoked agents, AATs, and sessions
Discovery: Token Issuers and proxies look up agent identities

8.2 Agent Identity Document (AID)

The AID is a JSON document that defines an agent’s cryptographic identity:

{
  "aid_version": "aip/v1alpha3",
  "agent_id": "<globally-unique-identifier>",
  "name": "<human-readable-name>",
  "description": "<agent-description>",
  "created_at": "<ISO-8601>",
  "status": "active",

  "public_key": {
    "kty": "EC",
    "crv": "P-256",
    "x": "...",
    "y": "...",
    "kid": "<key-id>",
    "use": "sig"
  },

  "metadata": {
    "platform": "<agent-platform>",
    "version": "<agent-version>",
    "owner": "<owner-email-or-org>",
    "tags": ["<tag>", ...]
  },

  "registry_attestation": {
    "registry_id": "<registry-identifier>",
    "signed_at": "<ISO-8601>",
    "expires_at": "<ISO-8601>",
    "signature": "<base64url-encoded-signature>"
  }
}

8.2.1 AID Fields

Field	Type	Required	Description
`aid_version`	string	Yes	MUST be `aip/v1alpha3`
`agent_id`	string	Yes	Globally unique identifier (UUID v4 or URI)
`name`	string	Yes	Human-readable name
`description`	string	No	Agent description
`created_at`	string	Yes	Registration time (ISO 8601)
`status`	string	Yes	`active`, `suspended`, or `revoked`
`public_key`	JWK	Yes	Agent’s public key in JWK format (RFC 7517)
`metadata`	object	No	Additional agent metadata
`registry_attestation`	object	Yes	Registry’s signature over the AID

8.2.2 Agent Status

Status	Description	AAT Issuance	AAT Validation
`active`	Agent is registered and operational	Allowed	Valid
`suspended`	Temporarily disabled (e.g., security review)	Blocked	Rejected
`revoked`	Permanently deactivated	Blocked	Rejected

8.2.3 Registry Attestation

The registry_attestation provides the registry’s cryptographic endorsement of the AID:

ATTEST_AID(aid, registry_key):
  aid_copy = COPY(aid)
  REMOVE aid_copy.registry_attestation
  canonical = JSON_CANONICALIZE(aid_copy)  # RFC 8785
  signature = SIGN(registry_key, canonical)
  RETURN {
    "registry_id": registry.id,
    "signed_at": now(),
    "expires_at": now() + attestation_ttl,
    "signature": base64url_encode(signature)
  }

8.3 Registry API

The AIP Registry exposes the following HTTP endpoints:

8.3.1 Agent Registration

POST /v1/agents HTTP/1.1
Host: registry.aip.example.com
Content-Type: application/json
Authorization: Bearer <registration-token>

{
  "name": "My AI Agent",
  "description": "Development assistant for code review",
  "public_key": {
    "kty": "EC",
    "crv": "P-256",
    "x": "...",
    "y": "..."
  },
  "metadata": {
    "platform": "cursor",
    "version": "1.0.0",
    "owner": "[email protected]"
  }
}

Response:

HTTP/1.1 201 Created
Content-Type: application/json

{
  "agent_id": "ag_550e8400-e29b-41d4-a716-446655440000",
  "aid": { ... },
  "registration_token_expires_at": "2026-03-19T00:00:00Z"
}

8.3.2 Agent Lookup

GET /v1/agents/{agent_id} HTTP/1.1
Host: registry.aip.example.com

Response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "agent_id": "ag_550e8400-e29b-41d4-a716-446655440000",
  "status": "active",
  "aid": { ... },
  "public_key": { ... }
}

8.3.3 Revocation List

GET /v1/revocations HTTP/1.1
Host: registry.aip.example.com
If-None-Match: "<etag>"

Response:

HTTP/1.1 200 OK
Content-Type: application/json
ETag: "<new-etag>"
Cache-Control: max-age=30

{
  "version": 42,
  "updated_at": "2026-02-19T10:30:00Z",
  "revoked_agents": [
    {
      "agent_id": "ag_...",
      "revoked_at": "2026-02-19T10:00:00Z",
      "reason": "Security incident"
    }
  ],
  "revoked_aats": [
    {
      "jti": "...",
      "revoked_at": "2026-02-19T10:15:00Z",
      "reason": "Token compromise"
    }
  ],
  "revoked_sessions": [
    {
      "session_id": "...",
      "revoked_at": "2026-02-19T10:20:00Z",
      "reason": "User logout"
    }
  ]
}

The revocation list supports conditional requests (ETag/If-None-Match) for efficient polling.

8.3.4 Agent Key Rotation

POST /v1/agents/{agent_id}/rotate-key HTTP/1.1
Host: registry.aip.example.com
Content-Type: application/json
Authorization: Bearer <agent-proof-of-possession>

{
  "new_public_key": {
    "kty": "EC",
    "crv": "P-256",
    "x": "...",
    "y": "..."
  }
}

Key rotation:

Agent generates new key pair
Agent signs rotation request with current private key (proof of possession)
Registry verifies signature, updates stored public key
Old key remains valid for key_grace_period (default: 1 hour)
New AID attestation issued

8.3.5 Registry JWKS

GET /v1/jwks HTTP/1.1
Host: registry.aip.example.com

Returns the registry’s public keys for verifying AID attestations:

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: public, max-age=3600

{
  "keys": [
    {
      "kty": "EC",
      "crv": "P-256",
      "kid": "registry-key-2026-02",
      "use": "sig",
      "alg": "ES256",
      "x": "...",
      "y": "..."
    }
  ]
}

8.4 Registry Security

8.4.1 Authentication

All registry API calls (except JWKS and health) MUST be authenticated.

Endpoint	Required Auth	Description
`POST /v1/agents`	Registration token	Initial agent registration
`GET /v1/agents/{id}`	Bearer token or mTLS	Agent lookup
`GET /v1/revocations`	Bearer token or mTLS	Revocation list
`POST /v1/agents/{id}/rotate-key`	Proof of possession	Key rotation
`GET /v1/jwks`	None (public)	Registry public keys

8.4.2 Rate Limiting

Implementations MUST rate-limit registration endpoints to prevent abuse.

8.4.3 Data Integrity

The registry MUST:

Store agent public keys with integrity protection (e.g., signed records)
Maintain an append-only audit log of all registration events
Never expose private keys (the registry never holds agent private keys)

9. Token Issuer (v1alpha3)

The Token Issuer validates agent identities and issues AATs.

9.1 Overview

The Token Issuer is a service that:

Validates an agent’s proof of possession (private key ownership)
Verifies the agent is registered and active in the AIP Registry
Binds the agent’s AAT to the authorizing user
Issues signed AATs with capabilities derived from policy

9.2 Token Issuance Flow

┌─────────┐          ┌──────────────┐          ┌──────────────┐
│  Agent   │          │ Token Issuer │          │ AIP Registry │
└────┬─────┘          └──────┬───────┘          └──────┬───────┘
     │                       │                         │
     │ 1. Token Request      │                         │
     │ (signed challenge)    │                         │
     ├──────────────────────▶│                         │
     │                       │ 2. Verify agent in      │
     │                       │    registry              │
     │                       ├────────────────────────▶│
     │                       │                         │
     │                       │ 3. Agent record +        │
     │                       │    revocation status     │
     │                       │◀────────────────────────┤
     │                       │                         │
     │                       │ 4. Verify proof of      │
     │                       │    possession            │
     │                       │                         │
     │                       │ 5. Verify user           │
     │                       │    authorization          │
     │                       │                         │
     │ 6. AAT                │                         │
     │◀──────────────────────┤                         │
     │                       │                         │

9.3 Token Request

9.3.1 Request Format

POST /v1/token HTTP/1.1
Host: issuer.aip.example.com
Content-Type: application/json

{
  "grant_type": "agent_authentication",
  "agent_id": "<agent-id>",
  "proof": {
    "type": "signed_challenge",
    "challenge": "<server-provided-challenge>",
    "signature": "<base64url-encoded-signature>",
    "algorithm": "ES256"
  },
  "user_authorization": {
    "type": "oauth2_token",
    "token": "<user-oauth-access-token>"
  },
  "requested_capabilities": {
    "tools": ["read_file", "list_directory", "git_status"],
    "resource_scopes": ["repo:read"],
    "allowed_servers": ["mcp://localhost:8080"]
  },
  "audience": "<target-proxy-or-server>"
}

9.3.2 Grant Types

Grant Type	Description	Use Case
`agent_authentication`	Agent proves identity + user authorization	Standard flow
`aat_refresh`	Refresh existing AAT	Token renewal
`agent_attestation`	Platform attestation (no user)	Autonomous agents

9.3.3 Proof of Possession

The agent proves ownership of its private key by signing a challenge:

GENERATE_PROOF(agent_key, challenge):
  payload = {
    "challenge": challenge,
    "agent_id": agent.id,
    "timestamp": now()
  }
  canonical = JSON_CANONICALIZE(payload)
  signature = SIGN(agent_key.private, canonical)
  RETURN {
    "type": "signed_challenge",
    "challenge": challenge,
    "signature": base64url_encode(signature),
    "algorithm": agent_key.algorithm
  }

The Token Issuer:

Retrieves the agent’s public key from the AIP Registry
Verifies the challenge signature using that public key
Confirms the challenge was recently issued (prevents replay)

9.3.4 User Authorization Methods

Method	`user_authorization.type`	Description
OAuth 2.0	`oauth2_token`	User’s OAuth access token (RECOMMENDED)
OIDC ID Token	`oidc_id_token`	OpenID Connect ID token
API Key	`api_key`	User’s API key
Local Attestation	`local_user`	OS-level user identity (localhost only)

OAuth 2.0 flow (RECOMMENDED):

{
  "user_authorization": {
    "type": "oauth2_token",
    "token": "ya29.A0ARrdaM..."
  }
}

The Token Issuer validates the OAuth token against the identity provider and extracts the user_id claim. Local attestation (development / localhost):

{
  "user_authorization": {
    "type": "local_user",
    "uid": 501,
    "username": "developer",
    "hostname": "dev-machine.local"
  }
}

9.4 Token Response

9.4.1 Success Response

HTTP/1.1 200 OK
Content-Type: application/json

{
  "aat": "eyJhbGciOiJFUzI1NiIsInR5cCI6ImFhdCtqd3QiLCJraWQiOiJpc3N1ZXIta2V5LTIwMjYtMDIifQ...",
  "token_type": "aat+jwt",
  "expires_in": 3600,
  "refresh_token": "<opaque-refresh-token>",
  "capabilities_granted": {
    "tools": ["read_file", "list_directory", "git_status"],
    "resource_scopes": ["repo:read"]
  },
  "capabilities_denied": {
    "tools": [],
    "reason": "All requested capabilities granted"
  }
}

Field	Type	Description
`aat`	string	The signed Agent Authentication Token (JWT)
`token_type`	string	MUST be `aat+jwt`
`expires_in`	int	Token lifetime in seconds
`refresh_token`	string	Opaque token for AAT refresh (OPTIONAL)
`capabilities_granted`	object	Capabilities included in the AAT
`capabilities_denied`	object	Requested capabilities that were denied

9.4.2 Error Response

HTTP/1.1 400 Bad Request
Content-Type: application/json

{
  "error": "<error-code>",
  "error_description": "<human-readable>",
  "error_details": { ... }
}

Error Code	HTTP Status	Description
`invalid_request`	400	Malformed request
`invalid_proof`	401	Proof of possession verification failed
`agent_not_found`	404	Agent not registered in registry
`agent_suspended`	403	Agent is suspended
`agent_revoked`	403	Agent is revoked
`user_auth_failed`	401	User authorization verification failed
`capabilities_denied`	403	All requested capabilities denied
`issuer_error`	500	Internal issuer error

9.5 Capability Determination

The Token Issuer determines AAT capabilities based on:

DETERMINE_CAPABILITIES(requested, agent_record, user_permissions):
  # Start with requested capabilities
  granted = requested.tools

  # Intersect with agent's registered permissions (from registry)
  IF agent_record.allowed_tools IS NOT EMPTY:
    granted = INTERSECTION(granted, agent_record.allowed_tools)

  # Intersect with user's delegated permissions
  IF user_permissions.delegatable_tools IS NOT EMPTY:
    granted = INTERSECTION(granted, user_permissions.delegatable_tools)

  RETURN granted

The AAT capabilities represent the maximum set of tools the agent can invoke. The AIP Proxy MAY further restrict this based on local policy.

9.6 Token Issuer JWKS

Token Issuers MUST expose a JWKS endpoint for AAT signature verification:

GET /v1/jwks HTTP/1.1
Host: issuer.aip.example.com

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: public, max-age=3600

{
  "keys": [
    {
      "kty": "EC",
      "crv": "P-256",
      "kid": "issuer-key-2026-02",
      "use": "sig",
      "alg": "ES256",
      "x": "...",
      "y": "..."
    }
  ]
}

Proxies MUST cache JWKS responses and refresh when encountering unknown kid values.

10. User Binding and Delegation (v1alpha3)

This section defines how agent actions are cryptographically linked to the authorizing user.

10.1 Motivation

Without user binding:

Agent actions are indistinguishable from each other and from human actions
Compliance frameworks (SOC 2, GDPR, HIPAA) cannot attribute actions to responsible parties
Revocation of user access does not revoke their agents’ access

User binding solves these by embedding a verifiable link from every agent action back to the authorizing human.

10.2 Delegation Model

┌────────────┐     Grants Delegation     ┌────────────┐
│    User     │─────────────────────────▶│   Agent    │
│  (Human)    │                          │   (AI)     │
│             │     AAT carries:          │            │
│  user_id    │  - user_id               │  agent_id  │
│  auth_time  │  - auth_method           │  public_key│
│             │  - delegation_scope      │            │
└────────────┘                           └─────┬──────┘
                                               │
                                        Uses AAT for
                                        tool calls
                                               │
                                               ▼
                                        ┌────────────┐
                                        │ AIP Proxy  │
                                        │            │
                                        │ Verifies:  │
                                        │ - agent_id │
                                        │ - user_id  │
                                        │ - scope    │
                                        └────────────┘

10.3 Delegation Chain Verification

The AIP Proxy MUST verify the complete delegation chain:

VERIFY_DELEGATION_CHAIN(aat):
  # 1. Verify agent identity (AAT signature + registry check)
  IF NOT valid_aat_signature(aat):
    RETURN (INVALID, "signature_invalid")

  # 2. Verify user binding is present
  IF aat.user_binding IS EMPTY:
    RETURN (INVALID, "missing_user_binding")

  # 3. Verify user authentication freshness
  max_auth_age = configured_max_auth_age OR 86400  # 24h default
  IF now() - aat.user_binding.auth_time > max_auth_age:
    RETURN (INVALID, "user_auth_stale")

  # 4. Verify delegation scope covers the requested action
  IF aat.user_binding.delegation_scope == "read_only":
    IF requested_tool is write_operation:
      RETURN (INVALID, "delegation_scope_exceeded")

  RETURN (VALID, nil)

10.4 Audit Trail Integration

When an AAT with user binding is present, audit log entries MUST include:

{
  "timestamp": "2026-02-19T10:30:45.123Z",
  "direction": "upstream",
  "method": "tools/call",
  "tool": "write_file",
  "decision": "ALLOW",
  "policy_mode": "enforce",
  "violation": false,

  "agent_id": "ag_550e8400-e29b-41d4-a716-446655440000",
  "agent_name": "Cursor IDE Agent",
  "user_id": "[email protected]",
  "user_auth_method": "oidc",
  "delegation_scope": "tools",
  "aat_jti": "aat_660e8400-e29b-41d4-a716-446655440001",
  "aat_issuer": "https://issuer.aip.example.com",
  "session_id": "550e8400-e29b-41d4-a716-446655440000",
  "policy_hash": "a3c7f2e8d9b4f1e2c8a7d6f3e9b2c4f1..."
}

This audit record establishes:

Who authorized the action (user_id, auth_method)
What agent performed the action (agent_id, agent_name)
How the delegation was granted (delegation_scope)
When it happened (timestamp)
What was done (tool, arguments)
By whose authority the AAT was issued (aat_issuer)

10.5 User Binding Revocation

When a user’s authorization is revoked:

Token Issuer marks all AATs for that user as revoked
Registry propagates revocation to all proxies (via revocation list)
Proxies reject tool calls from revoked AATs

REVOKE_USER_DELEGATION(user_id):
  # Find all active AATs for this user
  affected_aats = FIND_AATS_BY_USER(user_id)

  FOR EACH aat IN affected_aats:
    ADD_TO_REVOCATION_LIST(aat.jti, "user_delegation_revoked")

  # Also revoke all sessions
  affected_sessions = FIND_SESSIONS_BY_USER(user_id)
  FOR EACH session IN affected_sessions:
    ADD_TO_REVOCATION_LIST(session.session_id, "user_delegation_revoked")

  LOG_REVOCATION_EVENT(user_id, affected_aats.count, affected_sessions.count)

11. Error Codes

AIP defines the following JSON-RPC error codes:

Code	Name	Description
-32001	Forbidden	Tool not in allowed_tools list
-32002	Rate Limited	Rate limit exceeded
-32004	User Denied	User rejected approval prompt
-32005	User Timeout	Approval prompt timed out
-32006	Method Not Allowed	JSON-RPC method not permitted
-32007	Protected Path	Access to protected path blocked
-32008	Token Required	Identity token required but not provided
-32009	Token Invalid	Identity token validation failed
-32010	Policy Signature Invalid	Policy signature verification failed
-32011	Token Revoked	Token or session explicitly revoked
-32012	Audience Mismatch	Token audience does not match expected value
-32013	Schema Mismatch	Tool schema hash does not match policy
-32014	DLP Redaction Failed	Request redaction produced invalid content
-32015	AAT Required	Agent Authentication Token required but not provided (new)
-32016	AAT Invalid	AAT validation failed (new)
-32017	AAT Capability Denied	Requested tool not in AAT capabilities (new)
-32018	Agent Not Registered	Agent not found in AIP Registry (new)
-32019	Delegation Expired	User delegation has expired or been revoked (new)
-32020	Issuer Untrusted	AAT issuer not in trusted_issuers list (new)

11.1 Error Response Format

{
  "jsonrpc": "2.0",
  "id": "<request_id>",
  "error": {
    "code": "<error_code>",
    "message": "<error_message>",
    "data": {
      "tool": "<tool_name>",
      "reason": "<human_readable_reason>"
    }
  }
}

11.2 New Error Codes (v1alpha3)

-32015 AAT Required

Returned when aat.require: true and no AAT is provided.

{
  "code": -32015,
  "message": "AAT required",
  "data": {
    "tool": "write_file",
    "reason": "Agent Authentication Token required for this proxy"
  }
}

-32016 AAT Invalid

Returned when AAT validation fails.

{
  "code": -32016,
  "message": "AAT invalid",
  "data": {
    "tool": "write_file",
    "reason": "AAT signature verification failed",
    "aat_error": "signature_invalid"
  }
}

Possible aat_error values:

malformed_aat - JWT structure invalid
unsupported_version - aat_version not recognized
untrusted_issuer - Issuer not in trusted list
unknown_signing_key - Issuer key not found
signature_invalid - Cryptographic signature failed
not_yet_valid - Token nbf is in the future
aat_expired - Token past expiration
audience_mismatch - Token audience wrong
aat_revoked - Token or session revoked
unknown_agent - Agent not in registry
agent_key_mismatch - Agent public key doesn’t match
agent_inactive - Agent suspended or revoked
replay_detected - JTI reuse detected

-32017 AAT Capability Denied

Returned when the requested tool is not in the AAT’s capabilities.

{
  "code": -32017,
  "message": "AAT capability denied",
  "data": {
    "tool": "delete_database",
    "reason": "Tool not in AAT capabilities",
    "agent_id": "ag_550e8400...",
    "granted_capabilities": ["read_file", "list_directory"]
  }
}

-32018 Agent Not Registered

Returned when the agent in the AAT is not found in the registry.

{
  "code": -32018,
  "message": "Agent not registered",
  "data": {
    "agent_id": "ag_unknown",
    "reason": "Agent not found in AIP Registry"
  }
}

-32019 Delegation Expired

Returned when the user binding in the AAT has expired.

{
  "code": -32019,
  "message": "Delegation expired",
  "data": {
    "tool": "write_file",
    "reason": "User delegation has expired",
    "user_auth_time": "2026-02-18T10:00:00Z",
    "max_auth_age": 86400
  }
}

-32020 Issuer Untrusted

Returned when the AAT was issued by an issuer not in the trusted_issuers list.

{
  "code": -32020,
  "message": "Issuer untrusted",
  "data": {
    "issuer": "https://unknown-issuer.example.com",
    "reason": "AAT issuer not in trusted_issuers configuration"
  }
}

12. Audit Log Format

12.1 Required Fields

Field	Type	Description
`timestamp`	ISO 8601	Time of the decision
`direction`	string	`upstream` (client->server) or `downstream` (server->client)
`decision`	string	`ALLOW`, `BLOCK`, `ALLOW_MONITOR`, `RATE_LIMITED`
`policy_mode`	string	`enforce` or `monitor`
`violation`	boolean	Whether a policy violation was detected

12.2 Optional Fields

Field	Type	Description
`method`	string	JSON-RPC method name
`tool`	string	Tool name (for tools/call)
`args`	object	Tool arguments (SHOULD be redacted)
`failed_arg`	string	Argument that failed validation
`failed_rule`	string	Regex pattern that failed
`session_id`	string	Session identifier
`token_id`	string	Identity token nonce
`policy_hash`	string	Policy hash at decision time
`agent_id`	string	Agent identifier (from AAT) (new)
`agent_name`	string	Human-readable agent name (from AAT) (new)
`user_id`	string	Authorizing user identifier (from AAT) (new)
`user_auth_method`	string	User authentication method (from AAT) (new)
`delegation_scope`	string	Delegation scope (from AAT) (new)
`aat_jti`	string	AAT unique identifier (new)
`aat_issuer`	string	Token Issuer identifier (new)

12.3 Example

{
  "timestamp": "2026-02-19T10:30:45.123Z",
  "direction": "upstream",
  "method": "tools/call",
  "tool": "delete_file",
  "args": {"path": "/etc/passwd"},
  "decision": "BLOCK",
  "policy_mode": "enforce",
  "violation": true,
  "failed_arg": "path",
  "failed_rule": "^/home/.*",
  "session_id": "550e8400-e29b-41d4-a716-446655440000",
  "agent_id": "ag_550e8400-e29b-41d4-a716-446655440000",
  "agent_name": "Cursor IDE Agent",
  "user_id": "[email protected]",
  "user_auth_method": "oidc",
  "delegation_scope": "tools",
  "aat_jti": "aat_660e8400-e29b-41d4-a716-446655440001",
  "aat_issuer": "https://issuer.aip.example.com",
  "policy_hash": "a3c7f2e8d9b4f1e2c8a7d6f3e9b2c4f1a8e7d3c2b5f4e9a7c3d8f2b6e1a9c4f7"
}

12.4 Identity Events

[Token issued/rotated/failed events remain unchanged from v1alpha2]

AAT Validated (v1alpha3)

{
  "timestamp": "2026-02-19T10:30:00.000Z",
  "event": "AAT_VALIDATED",
  "agent_id": "ag_550e8400...",
  "user_id": "[email protected]",
  "aat_jti": "aat_660e8400...",
  "issuer": "https://issuer.aip.example.com",
  "capabilities_granted": ["read_file", "list_directory"]
}

AAT Rejected (v1alpha3)

{
  "timestamp": "2026-02-19T10:30:00.000Z",
  "event": "AAT_REJECTED",
  "agent_id": "ag_550e8400...",
  "aat_jti": "aat_660e8400...",
  "error": "aat_expired",
  "tool": "write_file"
}

Registry Revocation Check (v1alpha3)

{
  "timestamp": "2026-02-19T10:30:00.000Z",
  "event": "REGISTRY_REVOCATION_CHECK",
  "mode": "cached",
  "revocation_list_version": 42,
  "agents_revoked": 3,
  "aats_revoked": 1,
  "sessions_revoked": 2
}

13. Conformance

13.1 Conformance Levels

Level	Requirements
Basic	Method authorization, tool allowlist, error codes
Full	Basic + argument validation, rate limiting, DLP, audit logging
Extended	Full + Human-in-the-Loop (action=ask)
Identity	Full + Identity tokens, session management
Server	Identity + Server-side validation endpoints
AAT	Server + AAT validation, registry integration (new)
Federation	AAT + Token Issuer, user binding, delegation chain (new)

13.2 Conformance Testing

Implementations MUST pass the conformance test suite to claim AIP compliance. The test suite consists of:

Schema validation tests: Verify policy parsing
Decision tests: Input -> expected decision
Normalization tests: Verify Unicode handling
Error format tests: Verify JSON-RPC errors
Identity tests: Token lifecycle, rotation, validation
Server tests: HTTP endpoint behavior
AAT tests: AAT structure, validation, capability checking (new)
Registry tests: Agent lookup, revocation checking (new)
Delegation tests: User binding verification, scope enforcement (new)

See spec/conformance/ for test vectors.

13.3 Implementation Requirements

Implementations MUST:

Parse apiVersion: aip.io/v1alpha3 documents
Reject documents with unknown apiVersion
Apply NFKC normalization to names
Return specified error codes
Support enforce and monitor modes

Implementations SHOULD:

Log decisions in the specified format
Support DLP scanning
Support rate limiting
Support identity tokens (for Identity conformance level)
Support AAT validation (for AAT conformance level)

Implementations MAY:

Use any regex engine with RE2 semantics
Implement additional security features (egress control, sandboxing)
Implement server-side validation (for Server conformance level)
Implement a Token Issuer (for Federation conformance level)
Implement a Registry (for Federation conformance level)

14. Security Considerations

14.0 Threat Model

[Section 14.0.1-14.0.3 remain unchanged from v1alpha2 with AAT additions]

14.0.1 Trust Boundaries

┌─────────────────────────────────────────────────────────────────┐
│                         UNTRUSTED                               │
│  ┌──────────┐                                                   │
│  │  Agent   │  AI agent may be manipulated via prompt injection │
│  └────┬─────┘                                                   │
│       │                                                         │
├───────┼─────────────────────────────────────────────────────────┤
│       │              TRUST BOUNDARY (AIP)                       │
│       ▼                                                         │
│  ┌──────────────┐                                               │
│  │ AIP Policy   │  Policy engine is TRUSTED                     │
│  │   Engine     │  Policy file integrity assumed                │
│  └──────┬───────┘                                               │
│         │                                                       │
├─────────┼───────────────────────────────────────────────────────┤
│         │              TRUST BOUNDARY (MCP)                     │
│         ▼                                                       │
│  ┌──────────────┐                                               │
│  │  MCP Server  │  Server behavior is UNTRUSTED                 │
│  │              │  Tool definitions may be malicious            │
│  └──────────────┘                                               │
│                          UNTRUSTED                              │
└─────────────────────────────────────────────────────────────────┘

Component	Trust Level	Rationale
User	Trusted	Defines policy, approves sensitive operations
Policy file	Trusted	Integrity verified via signature
AIP Engine	Trusted	Assumed correctly implemented
AIP Registry	Trusted	Root of trust for agent identities (new)
Token Issuer	Trusted	Issues AATs based on verified identity (new)
Agent (LLM)	Untrusted	Subject to prompt injection, jailbreaks
Agent’s AAT	Conditionally Trusted	Trusted only after cryptographic verification (new)
MCP Server	Untrusted	May be malicious or compromised
Tool definitions	Untrusted	May contain poisoned descriptions

14.0.2 Threats In Scope (v1alpha3 additions)

Threat	Attack Vector	AIP Mitigation
AAT theft	Stolen AAT used by different agent	Agent key thumbprint verification, JTI replay prevention
AAT forgery	Attacker creates fake AAT	Cryptographic signature verification via issuer JWKS
User impersonation	Agent claims different user	User binding verified through Token Issuer’s auth flow
Capability escalation	Agent requests tools beyond delegation	Capability intersection with local policy
Registry poisoning	Attacker modifies agent records	Registry attestation signatures, mTLS
Issuer compromise	Attacker issues unauthorized AATs	Trusted issuer list, key rotation, revocation
Delegation abuse	Agent acts beyond user’s intent	Delegation scope enforcement, short-lived AATs

14.0.3 Defense in Depth (v1alpha3)

Request Flow:

  Agent Request (with AAT)
       │
       ▼
  ┌────────────────┐
  │ 1. Method      │  Block unauthorized JSON-RPC methods
  │    Check       │
  └───────┬────────┘
          │
          ▼
  ┌────────────────┐
  │ 2. AAT         │  Verify signature, issuer, expiry,
  │    Validation  │  agent identity, user binding
  │    (v1alpha3)  │  Check registry revocation list
  └───────┬────────┘
          │
          ▼
  ┌────────────────┐
  │ 3. AAT         │  Check AAT capabilities against
  │    Capability  │  requested tool
  │    Check       │
  └───────┬────────┘
          │
          ▼
  ┌────────────────┐
  │ 4. Identity    │  Validate session token, binding
  │    Check       │
  └───────┬────────┘
          │
          ▼
  ┌────────────────┐
  │ 5. Rate Limit  │  Prevent resource exhaustion
  │    Check       │
  └───────┬────────┘
          │
          ▼
  ┌────────────────┐
  │ 6. Tool        │  Allowlist enforcement
  │    Check       │
  └───────┬────────┘
          │
          ▼
  ┌────────────────┐
  │ 7. Argument    │  Regex validation, protected paths
  │    Check       │
  └───────┬────────┘
          │
          ▼
  ┌────────────────┐
  │ 8. HITL        │  Human approval for sensitive ops
  │    (if ask)    │
  └───────┬────────┘
          │
          ▼
     MCP Server
          │
          ▼
  ┌────────────────┐
  │ 9. DLP         │  Redact sensitive response data
  │    Scan        │
  └───────┬────────┘
          │
          ▼
     Agent Response

14.1 Policy File Protection

The policy file itself MUST be protected from modification by the agent. Implementations MUST automatically add the policy file path to protected_paths.

14.2 Regex Denial of Service (ReDoS)

Implementations MUST use a regex engine that guarantees linear-time matching (RE2 or equivalent).

14.3 Unicode Normalization

Implementations MUST apply NFKC normalization to prevent homoglyph attacks.

14.4 Monitor Mode Risks

Monitor mode allows all requests through. Implementations SHOULD warn users when monitor mode is enabled in production environments.

14.5 Audit Log Integrity

Audit logs SHOULD be written to a location not writable by the agent.

14.6 Identity Token Security

[Remains unchanged from v1alpha2]

14.7 Server Endpoint Security

[Remains unchanged from v1alpha2]

14.8 AAT Security (v1alpha3)

14.8.1 AAT Storage

AATs SHOULD be stored in memory only, not persisted to disk. If persistence is required, AATs MUST be encrypted at rest. The _aip_aat field in JSON-RPC params MUST be stripped before any logging or forwarding.

14.8.2 AAT Transmission

AATs transmitted over the network MUST use TLS 1.2 or later. Implementations MUST NOT send AATs over unencrypted connections. For HTTP transport, AATs MUST be sent as headers (not query parameters or request body) to prevent leakage in server logs.

14.8.3 AAT Lifetime

AAT lifetimes SHOULD be limited:

Environment	Recommended `exp - iat`	Rationale
Interactive (IDE)	1 hour	Session-length
Batch processing	Duration of job	Tight scoping
Long-running service	15 minutes (with refresh)	Minimize theft window
CI/CD pipeline	Duration of pipeline	Job-scoped

Implementations SHOULD reject AATs with lifetime greater than 24 hours.

14.8.4 Replay Prevention

AAT replay prevention uses the jti (JWT ID) claim:

ATOMIC_CHECK_AND_RECORD_JTI(jti):
  # Same atomic semantics as nonce checking
  IF ATOMIC_SET_IF_NOT_EXISTS(jti, ttl=max_token_age):
    RETURN TRUE   # JTI was new
  ELSE:
    RETURN FALSE  # JTI already seen (replay attempt)

JTI storage requirements follow the same guidelines as nonce storage (Section 5 / v1alpha2).

14.8.5 Registry Trust

The AIP Registry is a high-value target. Implementations MUST:

Use TLS for all registry communications
Verify the registry’s TLS certificate
Support mTLS for registry authentication
Cache registry responses with bounded TTL
Have a fallback strategy when the registry is unreachable (see failover_mode)

14.8.6 Token Issuer Trust

Token Issuers control what capabilities agents receive. Compromised issuers can grant excessive permissions. Mitigations:

Use trusted_issuers to limit accepted issuers
Intersect AAT capabilities with local policy (capabilities_mode: "intersect")
Monitor aip_aat_validations_total for anomalies
Implement issuer key rotation and revocation

15. IANA Considerations

This specification requests registration of the following:

15.1 Media Type

Type name: application
Subtype name: vnd.aip.policy+yaml
Required parameters: None
File extension: .yaml, .yml

15.2 URI Scheme

This specification uses the aip.io namespace for versioning:

aip.io/v1alpha1 - Initial specification
aip.io/v1alpha2 - Identity and server-side validation
aip.io/v1alpha3 - This specification (AAT, Registry, Token Issuer)

15.3 JWT Type Header (v1alpha3)

typ: aat+jwt for Agent Authentication Tokens

Appendix A: Complete Schema Reference

# Complete AgentPolicy schema (v1alpha3)

apiVersion: aip.io/v1alpha3      # REQUIRED
kind: AgentPolicy                 # REQUIRED

metadata:                         # REQUIRED
  name: string                    # REQUIRED - Policy identifier
  version: string                 # OPTIONAL - Semantic version
  owner: string                   # OPTIONAL - Contact email
  signature: string               # OPTIONAL - Policy signature

spec:                             # REQUIRED
  mode: enforce | monitor         # OPTIONAL, default: enforce

  allowed_tools:                  # OPTIONAL
    - string

  allowed_methods:                # OPTIONAL
    - string

  denied_methods:                 # OPTIONAL
    - string

  protected_paths:                # OPTIONAL
    - string

  strict_args_default: boolean    # OPTIONAL, default: false

  tool_rules:                     # OPTIONAL
    - tool: string                # REQUIRED
      action: allow|block|ask     # OPTIONAL, default: allow
      rate_limit: string          # OPTIONAL, format: "N/period"
      strict_args: boolean        # OPTIONAL
      schema_hash: string         # OPTIONAL - Tool schema integrity
      allow_args:                 # OPTIONAL
        <arg_name>: <regex>

  dlp:                            # OPTIONAL
    enabled: boolean              # OPTIONAL, default: true
    scan_requests: boolean        # OPTIONAL, default: false
    scan_responses: boolean       # OPTIONAL, default: true
    detect_encoding: boolean      # OPTIONAL, default: false
    filter_stderr: boolean        # OPTIONAL, default: false
    max_scan_size: string         # OPTIONAL, default: "1MB"
    on_request_match: string      # OPTIONAL, default: "block"
    on_redaction_failure: string  # OPTIONAL, default: "block"
    log_original_on_failure: boolean  # OPTIONAL, default: false
    patterns:                     # REQUIRED if dlp present
      - name: string              # REQUIRED
        regex: string             # REQUIRED
        scope: string             # OPTIONAL, default: "all"

  identity:                       # OPTIONAL
    enabled: boolean              # OPTIONAL, default: false
    token_ttl: string             # OPTIONAL, default: "5m"
    rotation_interval: string     # OPTIONAL, default: "4m"
    require_token: boolean        # OPTIONAL, default: false
    session_binding: string       # OPTIONAL, default: "process"
    nonce_window: string          # OPTIONAL, default: equals token_ttl
    policy_transition_grace: string  # OPTIONAL, default: "0s"
    audience: string              # OPTIONAL, default: metadata.name
    nonce_storage:                # OPTIONAL
      type: string                # memory | redis | postgres
      address: string
      key_prefix: string          # default: "aip:nonce:"
      clock_skew_tolerance: string  # default: "30s"
    keys:                         # OPTIONAL
      signing_algorithm: string   # default: "ES256"
      key_source: string          # generate | file | external
      key_path: string
      rotation_period: string     # default: "7d"
      jwks_endpoint: string       # default: "/v1/jwks"

  server:                         # OPTIONAL
    enabled: boolean              # OPTIONAL, default: false
    listen: string                # OPTIONAL, default: "127.0.0.1:9443"
    failover_mode: string         # OPTIONAL, default: "fail_closed"
    timeout: string               # OPTIONAL, default: "5s"
    tls:
      cert: string
      key: string
    fail_open_constraints:        # OPTIONAL
      allowed_tools:
        - string
      max_duration: string
      max_requests: integer
      alert_webhook: string
      require_local_policy: boolean
    endpoints:                    # OPTIONAL
      validate: string            # default: "/v1/validate"
      revoke: string              # default: "/v1/revoke"
      jwks: string                # default: "/v1/jwks"
      health: string              # default: "/health"
      metrics: string             # default: "/metrics"

  registry:                       # OPTIONAL (v1alpha3)
    enabled: boolean              # OPTIONAL, default: false
    endpoint: string              # REQUIRED if enabled
    tls:
      ca_cert: string
      client_cert: string
      client_key: string
    cache:
      enabled: boolean            # default: true
      ttl: string                 # default: "5m"
      max_entries: integer        # default: 10000
    revocation:
      check_interval: string      # default: "30s"
      mode: string                # online | cached | crl
      crl_path: string
    auth:
      type: string                # bearer | mtls | api_key
      token: string
      api_key: string

  aat:                            # OPTIONAL (v1alpha3)
    enabled: boolean              # OPTIONAL, default: false
    require: boolean              # OPTIONAL, default: false
    validation:
      verify_signature: boolean   # default: true
      verify_user_binding: boolean  # default: true
      verify_capabilities: boolean  # default: true
      max_token_age: string       # default: "1h"
      clock_skew: string          # default: "30s"
    capabilities_mode: string     # intersect | aat_only | policy_only
    trusted_issuers:              # OPTIONAL
      - string
    header_name: string           # default: "X-AIP-AAT"

Appendix B: Changelog

v1alpha3 (2026-02-19)

Agent Authentication Token (AAT)

Added Section 7: Agent Authentication Token specification
- JWT-based AAT structure with agent, user_binding, capabilities, and context claims
- AAT signing requirements (ES256, EdDSA, RS256; no symmetric algorithms)
- AAT lifecycle: issuance, refresh, validation, revocation
- AAT transport via _aip_aat JSON-RPC param or X-AIP-AAT HTTP header
- AAT validation algorithm with 9-step verification
- JTI-based replay prevention
Added aat configuration section (Section 3.10)
- capabilities_mode: intersect, aat_only, policy_only
- trusted_issuers for issuer allowlisting
- Configurable validation strictness

AIP Registry

Added Section 8: AIP Registry specification
- Agent Identity Document (AID) structure with registry attestation
- Registry API: registration, lookup, revocation list, key rotation, JWKS
- Agent status lifecycle: active, suspended, revoked
- Registry attestation via Ed25519/ES256 signatures
Added registry configuration section (Section 3.9)
- Revocation modes: online, cached, CRL
- Cache configuration for agent keys and revocation status
- mTLS and bearer token authentication

Token Issuer

Added Section 9: Token Issuer specification
- Token issuance flow with proof of possession
- Grant types: agent_authentication, aat_refresh, agent_attestation
- User authorization methods: OAuth 2.0, OIDC, API key, local attestation
- Capability determination from agent record, user permissions, and requested capabilities
- Token Issuer JWKS endpoint

User Binding and Delegation

Added Section 10: User Binding and Delegation specification
- Delegation model connecting users to agents to actions
- Delegation chain verification algorithm
- Delegation scope enforcement (full, tools, read_only, session, custom)
- User binding revocation propagation
- Audit trail integration with user identity

Evaluation Semantics

Updated tool-level authorization (Section 4.3) with AAT capability checks
- Step 0b: AAT validation
- Step 0c: AAT capability intersection
Added AAT_REQUIRED, AAT_INVALID, AAT_CAPABILITY_DENIED decision outcomes

Error Codes

Added -32015 AAT Required
Added -32016 AAT Invalid (with 13 detailed error subtypes)
Added -32017 AAT Capability Denied
Added -32018 Agent Not Registered
Added -32019 Delegation Expired
Added -32020 Issuer Untrusted

Metrics

Added aip_aat_validations_total counter
Added aip_registry_checks_total counter
Added aip_registry_latency_seconds histogram
Added aip_active_agents gauge

Audit Logging

Added AAT-enriched audit log fields (agent_id, agent_name, user_id, user_auth_method, delegation_scope, aat_jti, aat_issuer)
Added AAT_VALIDATED, AAT_REJECTED, REGISTRY_REVOCATION_CHECK event types

Security

Updated threat model with AAT-specific threats (theft, forgery, impersonation, capability escalation, registry poisoning, issuer compromise, delegation abuse)
Added Section 14.8: AAT Security (storage, transmission, lifetime, replay prevention, registry trust, issuer trust)
Defense in depth expanded to 9 layers (added AAT validation, AAT capability check)

Conformance

Added AAT conformance level
Added Federation conformance level
Added AAT, registry, and delegation test categories

v1alpha2 (2026-01-24)

Added identity configuration section (token generation, rotation, session binding)
Added server-side validation endpoints
Added schema_hash for tool poisoning prevention
Added DLP enhancements (scan_requests, max_scan_size, on_request_match)
Added threat model (Section 10.0)
Added policy signature (metadata.signature)
Added error codes -32008 through -32014
Added Identity and Server conformance levels

v1alpha1 (2026-01-20)

Initial draft specification
Defined core policy schema
Defined evaluation semantics
Defined error codes
Defined audit log format

Appendix C: References

Appendix D: Future Extensions

This appendix describes features under consideration for future versions of AIP.

D.1 Network Egress Control

Status: Proposed for v1beta1

D.2 Policy Inheritance

Status: Under Discussion Allow policies to extend base policies:

apiVersion: aip.io/v1beta1
kind: AgentPolicy
metadata:
  name: team-policy
spec:
  extends: "org-base-policy"
  allowed_tools:
    - additional_tool

D.3 External Identity Federation

Status: Proposed for v1beta1 Allow policies to integrate with external identity providers:

spec:
  identity:
    federation:
      type: oidc
      issuer: "https://accounts.google.com"
      client_id: "aip-agent"
      required_claims:
        email_verified: true
        hd: "company.com"

Supported federation types:

oidc - OpenID Connect providers
spiffe - SPIFFE/SPIRE workload identity

D.4 Telemetry and Metrics

Status: Partially implemented in v1alpha2/v1alpha3 (metrics endpoint)

D.5 Advanced Policy Expressions

Status: Under Discussion Support for CEL (Common Expression Language) or Rego for complex validation:

tool_rules:
  - tool: file_write
    action: allow
    when: |
      args.path.startsWith("/allowed/") &&
      !args.path.contains("..") &&
      size(args.content) < 1048576

D.6 Agentic JWT Compatibility

Status: Under Discussion for v1beta1 Full compatibility with the Agentic JWT specification. Mapping to Agentic JWT claims:

AIP Field	Agentic JWT Claim
`aat.agent.id`	`sub` (subject)
`aat.context.policy_hash`	`agent_proof.agent_checksum`
`aat.context.session_id`	`intent.workflow_id`
`aat.capabilities.tools`	Workflow steps
`aat.user_binding.user_id`	`azp` (authorized party)

D.7 Multi-Agent Delegation (v1alpha3 future)

Status: Under Discussion Support for agent-to-agent delegation chains, where Agent A (with user authorization) delegates a subset of capabilities to Agent B:

{
  "delegation_chain": [
    {
      "delegator": "[email protected]",
      "delegatee": "ag_agent-a",
      "scope": "tools"
    },
    {
      "delegator": "ag_agent-a",
      "delegatee": "ag_agent-b",
      "scope": "read_only"
    }
  ]
}

Constraints:

Each delegation step MUST reduce or maintain scope (never escalate)
Maximum chain depth: 3 (user -> agent -> sub-agent)
All delegators must be active and non-revoked

D.8 Registry Federation

Status: Under Discussion Allow multiple registries to federate, enabling cross-organization agent identity verification:

registry:
  federation:
    trusted_registries:
      - id: "partner-registry"
        endpoint: "https://registry.partner.com"
        trust_level: "tools_only"  # Only trust tool capabilities

Appendix E: Implementation Notes

E.1 Reference Implementation

The reference implementation is available at: https://github.com/openagentidentityprotocol/aip-go It provides:

Go-based proxy (aip-proxy)
Policy engine (pkg/policy)
DLP scanner (pkg/dlp)
Audit logger (pkg/audit)
Identity manager (pkg/identity)
HTTP server (pkg/server)
AAT validator (pkg/aat) (v1alpha3)
Registry client (pkg/registry) (v1alpha3)

E.2 Testing Against Conformance Suite

# Clone the spec repository
git clone https://github.com/openagentidentityprotocol/agentidentityprotocol

# Run conformance tests against your implementation
cd agentidentityprotocol/spec/conformance
./run-tests.sh --impl "your-aip-binary" --level "aat"

E.3 AAT Implementation Guidance

Generating Agent Key Pair

import (
    "crypto/ecdsa"
    "crypto/elliptic"
    "crypto/rand"
)

func generateAgentKeyPair() (*ecdsa.PrivateKey, error) {
    return ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
}

Computing JWK Thumbprint (RFC 7638)

import (
    "crypto/sha256"
    "encoding/json"
)

func jwkThumbprint(jwk map[string]interface{}) string {
    // For EC keys: {"crv":"...","kty":"EC","x":"...","y":"..."}
    required := map[string]interface{}{
        "crv": jwk["crv"],
        "kty": jwk["kty"],
        "x":   jwk["x"],
        "y":   jwk["y"],
    }
    canonical, _ := json.Marshal(required)
    hash := sha256.Sum256(canonical)
    return base64url(hash[:])
}

Validating an AAT

func validateAAT(tokenString string, trustedIssuers []string, registry RegistryClient) (*AATClaims, error) {
    // 1. Parse JWT header (don't verify yet)
    header, err := parseJWTHeader(tokenString)
    if err != nil {
        return nil, fmt.Errorf("malformed_aat: %w", err)
    }

    // 2. Get issuer's public key via JWKS
    issuerKey, err := getIssuerKey(header.Kid, trustedIssuers)
    if err != nil {
        return nil, fmt.Errorf("unknown_signing_key: %w", err)
    }

    // 3. Verify signature
    claims, err := jwt.ParseWithClaims(tokenString, &AATClaims{}, func(t *jwt.Token) (interface{}, error) {
        return issuerKey, nil
    })
    if err != nil {
        return nil, fmt.Errorf("signature_invalid: %w", err)
    }

    // 4. Check registry for agent status and revocation
    agent, err := registry.GetAgent(claims.Agent.ID)
    if err != nil {
        return nil, fmt.Errorf("unknown_agent: %w", err)
    }
    if agent.Status != "active" {
        return nil, fmt.Errorf("agent_inactive: %s", agent.Status)
    }

    // 5. Verify agent key thumbprint
    if agent.PublicKeyThumbprint != claims.Agent.PublicKeyThumbprint {
        return nil, fmt.Errorf("agent_key_mismatch")
    }

    // 6. Check JTI for replay
    if !atomicRecordJTI(claims.JTI) {
        return nil, fmt.Errorf("replay_detected")
    }

    return claims, nil
}

E.4 Registering Your Implementation

Implementations that pass the conformance suite may be listed in the official registry. Submit a PR to the AIP repository with:

Implementation name and URL
Conformance level achieved (Basic/Full/Extended/Identity/Server/AAT/Federation)
Platform support matrix

​Agent Identity Protocol (AIP) Specification

​Abstract

​Table of Contents

​1. Introduction

​1.1 Motivation

​1.2 Goals

​1.3 Non-Goals

​1.4 Relationship to MCP

​1.5 Relationship to MCP Authorization

​1.6 Two-Layer Architecture (v1alpha3)

​2. Terminology

​3. Policy Document Schema

​3.1 Document Structure

​3.2 Required Fields

​3.3 Metadata

​3.3.1 Policy Signature

​3.4 Spec Fields

​3.4.1 mode

​3.4.2 allowed_tools

​3.4.3 allowed_methods

​3.4.4 denied_methods

​3.4.5 protected_paths

​3.4.6 strict_args_default

​3.5 Tool Rules

​3.5.1 Actions

​3.5.2 Rate Limiting

​3.5.3 Argument Validation

​3.5.4 Tool Schema Hashing

​3.6 DLP Configuration

​3.7 Identity Configuration

​3.8 Server Configuration

​3.9 Registry Configuration (v1alpha3)

​3.9.1 enabled

​3.9.2 endpoint

​3.9.3 Revocation Modes

​3.9.4 Cache Configuration

​3.10 AAT Configuration (v1alpha3)

​3.10.1 enabled

​3.10.2 require

​3.10.3 capabilities_mode

​3.10.4 trusted_issuers

​3.10.5 header_name

​4. Evaluation Semantics

​4.1 Name Normalization

​4.2 Method-Level Authorization

​4.3 Tool-Level Authorization

​4.4 Decision Outcomes

​4.5 Argument Validation

​5. Agent Identity

​5.1 Overview

​5.2 Policy Hash

​5.2.1 Canonical Form

​5.2.2 Hash Computation

​5.3 Identity Token Structure

​5.4 Token Lifecycle

​5.5 Session Management

​5.6 Token and Session Revocation

​5.7 Compatibility with Agentic JWT

​5.8 Key Management

​6. Server-Side Validation

​6.1 Overview

​6.2 Validation Endpoint

​6.2.1 Request Format

​6.2.2 Response Format

​6.3 Health Endpoint

​6.4 Metrics Endpoint

​6.5 Revocation Endpoint

​6.6 Authentication

​7. Agent Authentication Token (AAT) (v1alpha3)

​7.1 Overview

​7.2 AAT Structure

​7.3 AAT Claims

​7.3.1 Standard JWT Claims

​7.3.2 Agent Claims

​7.3.3 User Binding Claims

​7.3.4 Capabilities Claims

​7.3.5 Context Claims

​7.4 AAT Signing

​7.5 AAT Lifecycle

​7.5.1 AAT Issuance

Agent Identity Protocol (AIP) Specification

Abstract

Table of Contents

1. Introduction

1.1 Motivation

1.2 Goals

1.3 Non-Goals

1.4 Relationship to MCP

1.5 Relationship to MCP Authorization

1.6 Two-Layer Architecture (v1alpha3)

2. Terminology

3. Policy Document Schema

3.1 Document Structure

3.2 Required Fields

3.3 Metadata

3.3.1 Policy Signature

3.4 Spec Fields

3.4.1 mode

3.4.2 allowed_tools

3.4.3 allowed_methods

3.4.4 denied_methods

3.4.5 protected_paths

3.4.6 strict_args_default

3.5 Tool Rules

3.5.1 Actions

3.5.2 Rate Limiting

3.5.3 Argument Validation

3.5.4 Tool Schema Hashing

3.6 DLP Configuration

3.7 Identity Configuration

3.8 Server Configuration

3.9 Registry Configuration (v1alpha3)

3.9.1 enabled

3.9.2 endpoint

3.9.3 Revocation Modes

3.9.4 Cache Configuration

3.10 AAT Configuration (v1alpha3)

3.10.1 enabled

3.10.2 require

3.10.3 capabilities_mode

3.10.4 trusted_issuers

3.10.5 header_name

4. Evaluation Semantics

4.1 Name Normalization

4.2 Method-Level Authorization

4.3 Tool-Level Authorization

4.4 Decision Outcomes

4.5 Argument Validation

5. Agent Identity

5.1 Overview

5.2 Policy Hash

5.2.1 Canonical Form

5.2.2 Hash Computation

5.3 Identity Token Structure

5.4 Token Lifecycle

5.5 Session Management

5.6 Token and Session Revocation

5.7 Compatibility with Agentic JWT

5.8 Key Management

6. Server-Side Validation

6.1 Overview

6.2 Validation Endpoint

6.2.1 Request Format

6.2.2 Response Format

6.3 Health Endpoint

6.4 Metrics Endpoint

6.5 Revocation Endpoint

6.6 Authentication

7. Agent Authentication Token (AAT) (v1alpha3)

7.1 Overview

7.2 AAT Structure

7.3 AAT Claims

7.3.1 Standard JWT Claims

7.3.2 Agent Claims

7.3.3 User Binding Claims

7.3.4 Capabilities Claims

7.3.5 Context Claims

7.4 AAT Signing

7.5 AAT Lifecycle

7.5.1 AAT Issuance