"""OAuth 2.0 Token Introspection (RFC 7662) provider for FastMCP. This module provides token verification for opaque tokens using the OAuth 2.0 Token Introspection protocol defined in RFC 7662. It allows FastMCP servers to validate tokens issued by authorization servers that don't use JWT format. Example: ```python from fastmcp import FastMCP from fastmcp.server.auth.providers.introspection import IntrospectionTokenVerifier # Verify opaque tokens via RFC 7662 introspection verifier = IntrospectionTokenVerifier( introspection_url="https://auth.example.com/oauth/introspect", client_id="your-client-id", client_secret="your-client-secret", required_scopes=["read", "write"] ) mcp = FastMCP("My Protected Server", auth=verifier) ``` """ from __future__ import annotations import base64 import contextlib import time from typing import Any, Literal, get_args import httpx from pydantic import AnyHttpUrl, SecretStr from fastmcp.server.auth import AccessToken, TokenVerifier from fastmcp.utilities.auth import parse_scopes from fastmcp.utilities.logging import get_logger from fastmcp.utilities.token_cache import TokenCache logger = get_logger(__name__) ClientAuthMethod = Literal["client_secret_basic", "client_secret_post"] class IntrospectionTokenVerifier(TokenVerifier): """ OAuth 2.0 Token Introspection verifier (RFC 7662). This verifier validates opaque tokens by calling an OAuth 2.0 token introspection endpoint. Unlike JWT verification which is stateless, token introspection requires a network call to the authorization server for each token validation. The verifier authenticates to the introspection endpoint using either: - HTTP Basic Auth (client_secret_basic, default): credentials in Authorization header - POST body authentication (client_secret_post): credentials in request body Both methods are specified in RFC 6749 (OAuth 2.0) and RFC 7662 (Token Introspection). Use this when: - Your authorization server issues opaque (non-JWT) tokens - You need to validate tokens from Auth0, Okta, Keycloak, or other OAuth servers - Your tokens require real-time revocation checking - Your authorization server supports RFC 7662 introspection Caching is disabled by default to preserve real-time revocation semantics. Set ``cache_ttl_seconds`` to enable caching and reduce load on the introspection endpoint (e.g., ``cache_ttl_seconds=300`` for 5 minutes). Example: ```python verifier = IntrospectionTokenVerifier( introspection_url="https://auth.example.com/oauth/introspect", client_id="my-service", client_secret="secret-key", required_scopes=["api:read"] ) ``` """ def __init__( self, *, introspection_url: str, client_id: str, client_secret: str | SecretStr, client_auth_method: ClientAuthMethod = "client_secret_basic", timeout_seconds: int = 10, required_scopes: list[str] | None = None, base_url: AnyHttpUrl | str | None = None, cache_ttl_seconds: int | None = None, max_cache_size: int | None = None, http_client: httpx.AsyncClient | None = None, ): """ Initialize the introspection token verifier. Args: introspection_url: URL of the OAuth 2.0 token introspection endpoint client_id: OAuth client ID for authenticating to the introspection endpoint client_secret: OAuth client secret for authenticating to the introspection endpoint client_auth_method: Client authentication method. "client_secret_basic" (default) uses HTTP Basic Auth header, "client_secret_post" sends credentials in POST body timeout_seconds: HTTP request timeout in seconds (default: 10) required_scopes: Required scopes for all tokens (optional) base_url: Base URL for TokenVerifier protocol cache_ttl_seconds: How long to cache introspection results in seconds. Caching is disabled by default (None) to preserve real-time revocation semantics. Set to a positive integer to enable caching (e.g., 300 for 5 minutes). max_cache_size: Maximum number of tokens to cache when caching is enabled. Default: 10000. http_client: Optional httpx.AsyncClient for connection pooling. When provided, the client is reused across calls and the caller is responsible for its lifecycle. When None (default), a fresh client is created per call. """ # Parse scopes if provided as string parsed_required_scopes = ( parse_scopes(required_scopes) if required_scopes is not None else None ) super().__init__(base_url=base_url, required_scopes=parsed_required_scopes) self.introspection_url = introspection_url self.client_id = client_id self.client_secret = ( client_secret.get_secret_value() if isinstance(client_secret, SecretStr) else client_secret ) # Validate client_auth_method to catch typos/invalid values early valid_methods = get_args(ClientAuthMethod) if client_auth_method not in valid_methods: options = " or ".join(f"'{m}'" for m in valid_methods) raise ValueError( f"Invalid client_auth_method: {client_auth_method!r}. " f"Must be {options}." ) self.client_auth_method: ClientAuthMethod = client_auth_method self.timeout_seconds = timeout_seconds self._http_client = http_client self.logger = get_logger(__name__) self._cache = TokenCache( ttl_seconds=cache_ttl_seconds, max_size=max_cache_size, ) def _create_basic_auth_header(self) -> str: """Create HTTP Basic Auth header value from client credentials.""" credentials = f"{self.client_id}:{self.client_secret}" encoded = base64.b64encode(credentials.encode("utf-8")).decode("utf-8") return f"Basic {encoded}" def _extract_scopes(self, introspection_response: dict[str, Any]) -> list[str]: """ Extract scopes from introspection response. RFC 7662 allows scopes to be returned as either: - A space-separated string in the 'scope' field - An array of strings in the 'scope' field (less common but valid) """ scope_value = introspection_response.get("scope") if scope_value is None: return [] # Handle string (space-separated) scopes if isinstance(scope_value, str): return [s.strip() for s in scope_value.split() if s.strip()] # Handle array of scopes if isinstance(scope_value, list): return [str(s) for s in scope_value if s] return [] async def verify_token(self, token: str) -> AccessToken | None: """ Verify a bearer token using OAuth 2.0 Token Introspection (RFC 7662). This method makes a POST request to the introspection endpoint with the token, authenticated using the configured client authentication method (client_secret_basic or client_secret_post). Results are cached in-memory to reduce load on the introspection endpoint. Cache TTL and size are configurable via constructor parameters. Args: token: The opaque token string to validate Returns: AccessToken object if valid and active, None if invalid, inactive, or expired """ # Check cache first is_cached, cached_result = self._cache.get(token) if is_cached: self.logger.debug("Token introspection cache hit") return cached_result try: async with ( contextlib.nullcontext(self._http_client) if self._http_client is not None else httpx.AsyncClient(timeout=self.timeout_seconds) ) as client: # Prepare introspection request per RFC 7662 # Build request data with token and token_type_hint data = { "token": token, "token_type_hint": "access_token", } # Build headers headers = { "Content-Type": "application/x-www-form-urlencoded", "Accept": "application/json", } # Add client authentication based on method if self.client_auth_method == "client_secret_basic": headers["Authorization"] = self._create_basic_auth_header() elif self.client_auth_method == "client_secret_post": data["client_id"] = self.client_id data["client_secret"] = self.client_secret response = await client.post( self.introspection_url, data=data, headers=headers, ) # Check for HTTP errors - don't cache HTTP errors (may be transient) if response.status_code != 200: self.logger.debug( "Token introspection failed: HTTP %d - %s", response.status_code, response.text[:200] if response.text else "", ) return None introspection_data = response.json() # Check if token is active (required field per RFC 7662) # Don't cache inactive tokens - they may become valid later # (e.g., tokens with future nbf, or propagation delays) if not introspection_data.get("active", False): self.logger.debug("Token introspection returned active=false") return None # Extract client_id (should be present for active tokens) client_id = introspection_data.get( "client_id" ) or introspection_data.get("sub", "unknown") # Extract expiration time exp = introspection_data.get("exp") if exp: # Validate expiration (belt and suspenders - server should set active=false) if exp < time.time(): self.logger.debug( "Token validation failed: expired token for client %s", client_id, ) return None # Extract scopes scopes = self._extract_scopes(introspection_data) # Check required scopes # Don't cache scope failures - permissions may be updated dynamically if self.required_scopes: token_scopes = set(scopes) required_scopes = set(self.required_scopes) if not required_scopes.issubset(token_scopes): self.logger.debug( "Token missing required scopes. Has: %s, Required: %s", token_scopes, required_scopes, ) return None # Create AccessToken with introspection response data result = AccessToken( token=token, client_id=str(client_id), scopes=scopes, expires_at=int(exp) if exp is not None else None, claims=introspection_data, # Store full response for extensibility ) self._cache.set(token, result) return result except httpx.TimeoutException: self.logger.debug( "Token introspection timed out after %d seconds", self.timeout_seconds ) return None except httpx.RequestError as e: self.logger.debug("Token introspection request failed: %s", e) return None except Exception as e: self.logger.debug("Token introspection error: %s", e) return None