authgent 0.3.4

Python SDK for authgent — IETF agent-identity stack: identity-chaining, transaction-tokens, RFC 8693 delegation, DPoP, MCP

authgent — Python SDK

The open-source identity SDK for AI agents. Token verification, delegation chain validation, DPoP sender-constrained tokens, and middleware for FastAPI and Flask.

Install

pip install authgent

# With FastAPI middleware
pip install authgent[fastapi]

# With Flask middleware
pip install authgent[flask]

Quick Start

Verify a Token

from authgent import verify_token

identity = await verify_token(
    token="eyJ...",
    issuer="http://localhost:8000",
)

print(identity.subject)           # "client:agnt_xxx"
print(identity.scopes)            # ["search:execute"]
print(identity.delegation_chain)  # DelegationChain(depth=0)

Validate Delegation Chains

from authgent import verify_token, verify_delegation_chain

identity = await verify_token(token=token, issuer="http://localhost:8000")

# Enforce: max 3 hops, must originate from a human
verify_delegation_chain(
    identity.delegation_chain,
    max_depth=3,
    require_human_root=True,
    allowed_actors=["client:agnt_trusted_orchestrator"],
)

Server API Client

from authgent import AgentAuthClient

client = AgentAuthClient("http://localhost:8000")

# Register an agent
agent = await client.register_agent(
    name="search-bot",
    scopes=["search:execute"],
)

# Get a token
token = await client.get_token(
    client_id=agent.client_id,
    client_secret=agent.client_secret,
    scope="search:execute",
)

# Delegate to another agent (token exchange)
delegated = await client.exchange_token(
    subject_token=token.access_token,
    audience="https://downstream-api.example.com",
    scopes=["read"],
    client_id=downstream_agent.client_id,
    client_secret=downstream_agent.client_secret,
)

# Introspect a token
info = await client.introspect_token(delegated.access_token)
print(info["active"])   # True
print(info["act"])      # {"sub": "client:agnt_search", "act": {"sub": "user:123"}}

# Revoke a token
await client.revoke_token(delegated.access_token)

DPoP (Sender-Constrained Tokens)

from authgent import DPoPClient

# Create an ephemeral key pair
dpop = DPoPClient.create()
print(dpop.jkt)  # JWK thumbprint for cnf binding

# Generate proof for a request
proof = dpop.create_proof(
    method="POST",
    url="https://api.example.com/data",
    access_token="eyJ...",
)
# Send as DPoP header alongside the access token

# Verify an incoming DPoP proof
from authgent import verify_dpop_proof

result = verify_dpop_proof(
    proof_jwt=request.headers["DPoP"],
    access_token=token,
    http_method="POST",
    http_uri="https://api.example.com/data",
)
print(result["jkt"])  # JWK thumbprint — must match token's cnf.jkt

Middleware

FastAPI

from fastapi import FastAPI, Depends, Request
from authgent.middleware.fastapi import AgentAuthMiddleware, get_agent_identity

app = FastAPI()
app.add_middleware(AgentAuthMiddleware, issuer="http://localhost:8000")

@app.post("/tools/search")
async def search(request: Request):
    identity = get_agent_identity(request)
    print(f"Agent: {identity.subject}")
    print(f"Scopes: {identity.scopes}")
    print(f"Delegation depth: {identity.delegation_chain.depth}")
    return {"results": [...]}

Flask

from flask import Flask, g
from authgent.middleware.flask import agent_auth_required

app = Flask(__name__)

@app.route("/tools/search", methods=["POST"])
@agent_auth_required(issuer="http://localhost:8000", scopes=["search:execute"])
def search():
    identity = g.agent_identity
    return {"agent": identity.subject}

MCP Scope Challenge

from authgent.middleware.scope_challenge import ScopeChallengeHandler

handler = ScopeChallengeHandler(
    server_url="http://localhost:8000",
    client_id="agnt_xxx",
    client_secret="sec_xxx",
)

# Automatically detect 403 scope challenges and trigger step-up
result = await handler.handle_scope_challenge(
    response=http_response,
    action="access_pii",
    scope="data:pii:read",
)

Adapters

MCP Server

from authgent.adapters.mcp import MCPAuthProvider

auth = MCPAuthProvider(server_url="http://localhost:8000")
identity = await auth.verify(token)

# Discovery URLs for MCP clients
auth.metadata_url  # http://localhost:8000/.well-known/oauth-authorization-server
auth.jwks_url      # http://localhost:8000/.well-known/jwks.json

Protected Resource Metadata (RFC 9728)

from authgent.adapters.protected_resource import ProtectedResourceMetadata

metadata = ProtectedResourceMetadata(
    resource="https://mcp-server.example.com",
    authorization_servers=["http://localhost:8000"],
    scopes_supported=["tools:execute", "db:read"],
)

# Serve at /.well-known/oauth-protected-resource
@app.get("/.well-known/oauth-protected-resource")
async def resource_metadata():
    return metadata.to_dict()

Error Handling

All SDK errors extend AuthgentError:

from authgent import (
    verify_token,
    AuthgentError,
    InvalidTokenError,
    DelegationError,
    DPoPError,
)

try:
    identity = await verify_token(token=token, issuer=issuer)
except InvalidTokenError as e:
    # Token expired, wrong issuer, bad signature
    print(f"Invalid token: {e}")
except DelegationError as e:
    # Chain too deep, unauthorized actor, scope escalation
    print(f"Delegation violation: {e}")
except DPoPError as e:
    # Proof mismatch, expired, wrong binding
    print(f"DPoP error: {e}")
except AuthgentError as e:
    # Any other SDK error
    print(f"Auth error: {e}")

API Reference

Core Functions

Function	Description
verify_token(token, issuer)	Verify JWT against issuer's JWKS, return AgentIdentity
verify_delegation_chain(chain, ...)	Enforce depth, actors, human root policies
verify_dpop_proof(proof_jwt, ...)	Verify DPoP proof-of-possession
DPoPClient.create()	Create ephemeral DPoP proof generator
AgentAuthClient(url)	Full server API client

Models

Class	Fields
AgentIdentity	subject, scopes, claims, delegation_chain
DelegationChain	depth, actors, human_root
TokenClaims	sub, scope, iss, exp, iat, jti, act, cnf

Middleware

Import	Framework
authgent.middleware.fastapi	FastAPI (ASGI)
authgent.middleware.flask	Flask (WSGI)
authgent.middleware.scope_challenge	MCP scope challenge handler

Adapters

Import	Purpose
authgent.adapters.mcp	MCP server auth provider
authgent.adapters.protected_resource	RFC 9728 metadata
authgent.adapters.langchain	LangChain tool auth

License

Apache 2.0