Nextcloud MCP Server

""" Unified Token Verifier for ADR-005 Token Audience Validation. This module replaces both NextcloudTokenVerifier and ProgressiveConsentTokenVerifier with a single implementation that supports two compliant OAuth modes: 1. Multi-audience mode (default): Validates MCP audience per RFC 7519 (resource servers validate only their own audience). Nextcloud independently validates its own audience. 2. Token exchange mode (opt-in): Tokens have MCP audience only, exchanged for Nextcloud tokens Key Design Principles: - Token verification happens HERE (validates MCP audience per OAuth spec) - Token exchange happens in context_helper.py (when creating NextcloudClient) - No token passthrough allowed (complies with MCP Security Specification) - Token reuse IS allowed for multi-audience tokens (RFC 8707) """ import hashlib import logging import time from typing import Any import httpx import jwt from jwt import PyJWKClient from mcp.server.auth.provider import AccessToken, TokenVerifier from nextcloud_mcp_server.config import Settings from nextcloud_mcp_server.observability.metrics import ( oauth_token_cache_hits_total, record_oauth_token_validation, ) logger = logging.getLogger(__name__) class UnifiedTokenVerifier(TokenVerifier): """ Unified token verifier supporting both multi-audience and token exchange modes. Compliant with MCP security specification - no token pass-through. This verifier: 1. Validates tokens using JWT verification with JWKS or introspection fallback 2. Enforces proper audience validation based on configured mode 3. Caches successful validations to avoid repeated API calls Mode Selection (via ENABLE_TOKEN_EXCHANGE setting): - False/omit (default): Multi-audience mode - validates MCP audience only (per RFC 7519). Nextcloud independently validates its own audience when receiving API calls. - True: Exchange mode - requires MCP audience only, then exchanges for Nextcloud token """ def __init__(self, settings: Settings): """ Initialize the unified token verifier. Args: settings: Application settings containing OAuth configuration """ self.settings = settings self.mode = "exchange" if settings.enable_token_exchange else "multi-audience" # Common components for all modes self.http_client = httpx.AsyncClient(timeout=10.0) # JWT verification support self.jwks_client: PyJWKClient | None = None if hasattr(settings, "jwks_uri") and settings.jwks_uri: logger.info(f"JWT verification enabled with JWKS URI: {settings.jwks_uri}") self.jwks_client = PyJWKClient(settings.jwks_uri, cache_keys=True) # Introspection support (for opaque tokens) self.introspection_uri: str | None = None if ( hasattr(settings, "introspection_uri") and settings.introspection_uri and settings.oidc_client_id and settings.oidc_client_secret ): self.introspection_uri = settings.introspection_uri logger.info(f"Token introspection enabled: {self.introspection_uri}") # Token cache: token_hash -> (userinfo, expiry_timestamp) self._token_cache: dict[str, tuple[dict[str, Any], float]] = {} self.cache_ttl = 3600 # 1 hour default logger.info( f"UnifiedTokenVerifier initialized in {self.mode} mode. " f"MCP audience: {settings.oidc_client_id} or {settings.nextcloud_mcp_server_url}, " f"Nextcloud resource URI: {settings.nextcloud_resource_uri}" ) async def verify_token(self, token: str) -> AccessToken | None: """ Verify token according to MCP TokenVerifier protocol. Per RFC 7519, we validate only MCP audience. The mode determines what happens AFTER verification in context_helper.py: - Multi-audience mode: Use token directly (Nextcloud validates its own audience) - Exchange mode: Exchange for Nextcloud-audience token via RFC 8693 Args: token: Bearer token to verify Returns: AccessToken if valid with MCP audience, None otherwise """ # Check cache first cached = self._get_cached_token(token) if cached: logger.debug("Token found in cache") oauth_token_cache_hits_total.labels(hit="true").inc() return cached oauth_token_cache_hits_total.labels(hit="false").inc() # Both modes do the same validation (MCP audience only) return await self._verify_mcp_audience(token) async def _verify_mcp_audience(self, token: str) -> AccessToken | None: """ Validate token has MCP audience. Per RFC 7519 Section 4.1.3, resource servers validate only their own presence in the audience claim. We don't validate Nextcloud's audience - that's Nextcloud's responsibility when it receives the token. Args: token: Bearer token to verify Returns: AccessToken if valid with MCP audience, None otherwise """ validation_method = "unknown" try: # Attempt JWT verification first if self._is_jwt_format(token) and self.jwks_client: validation_method = "jwt" payload = await self._verify_jwt_signature(token) if payload: record_oauth_token_validation("jwt", "valid") else: record_oauth_token_validation("jwt", "invalid") else: # Fall back to introspection for opaque tokens validation_method = "introspect" payload = await self._introspect_token(token) if payload: record_oauth_token_validation("introspect", "valid") else: record_oauth_token_validation("introspect", "invalid") if not payload: return None # Check payload is valid if not payload: return None # Validate MCP audience is present if not self._has_mcp_audience(payload): audiences = payload.get("aud", []) logger.error( f"Token rejected: Missing MCP audience. " f"Got {audiences}, need MCP ({self.settings.oidc_client_id} or " f"{self.settings.nextcloud_mcp_server_url})" ) # Record as invalid due to audience mismatch record_oauth_token_validation(validation_method, "invalid") return None # Log based on mode for clarity if self.mode == "multi-audience": logger.info( "MCP audience validated - token can be used directly " "(Nextcloud will validate its own audience)" ) else: logger.info( "MCP audience validated - token will be exchanged for Nextcloud access" ) return self._create_access_token(token, payload) except Exception as e: logger.error(f"Token verification failed: {e}") record_oauth_token_validation(validation_method, "error") return None def _has_mcp_audience(self, payload: dict[str, Any]) -> bool: """ Check if token has MCP audience. Per RFC 7519 Section 4.1.3, resource servers should only validate their own presence in the audience claim. We don't validate Nextcloud's audience - that's Nextcloud's responsibility when it receives the token. Args: payload: Decoded token payload Returns: True if MCP audience present, False otherwise """ audiences = payload.get("aud", []) if isinstance(audiences, str): audiences = [audiences] audiences_set = set(audiences) # MCP must have at least one: client_id OR server_url OR server_url/mcp return bool( self.settings.oidc_client_id in audiences_set or ( self.settings.nextcloud_mcp_server_url and ( self.settings.nextcloud_mcp_server_url in audiences_set or f"{self.settings.nextcloud_mcp_server_url}/mcp" in audiences_set ) ) ) def _is_jwt_format(self, token: str) -> bool: """ Check if token looks like a JWT (has 3 parts separated by dots). Args: token: The token to check Returns: True if token appears to be JWT format """ return "." in token and token.count(".") == 2 async def _verify_jwt_signature(self, token: str) -> dict[str, Any] | None: """ Verify JWT token with signature validation using JWKS. Args: token: JWT token to verify Returns: Decoded payload if valid, None if invalid """ try: assert self.jwks_client is not None # Caller should check before calling # Get signing key from JWKS signing_key = self.jwks_client.get_signing_key_from_jwt(token) # Verify and decode JWT # Note: We don't validate audience here - that's done separately based on mode payload = jwt.decode( token, signing_key.key, algorithms=["RS256"], issuer=( self.settings.oidc_issuer if hasattr(self.settings, "oidc_issuer") else None ), options={ "verify_signature": True, "verify_exp": True, "verify_iat": True, "verify_iss": ( True if hasattr(self.settings, "oidc_issuer") and self.settings.oidc_issuer else False ), "verify_aud": False, # We handle audience validation separately }, ) logger.debug(f"JWT signature verified for user: {payload.get('sub')}") return payload except jwt.ExpiredSignatureError: logger.info("JWT token has expired") return None except jwt.InvalidIssuerError as e: logger.warning(f"JWT issuer validation failed: {e}") return None except jwt.InvalidTokenError as e: logger.warning(f"JWT validation failed: {e}") return None except Exception as e: logger.error(f"Unexpected error during JWT verification: {e}") return None async def _introspect_token(self, token: str) -> dict[str, Any] | None: """ Validate token by calling the introspection endpoint (RFC 7662). Args: token: Bearer token to introspect Returns: Token payload if active, None if inactive or invalid """ if not self.introspection_uri: logger.debug("No introspection endpoint configured") return None try: # Introspection requires client authentication client_id = self.settings.oidc_client_id client_secret = self.settings.oidc_client_secret assert client_id is not None and client_secret is not None response = await self.http_client.post( self.introspection_uri, data={"token": token}, auth=(client_id, client_secret), ) if response.status_code == 200: introspection_data = response.json() # Check if token is active if not introspection_data.get("active", False): logger.info("Token introspection returned inactive=false") return None logger.debug( f"Token introspected successfully for user: {introspection_data.get('sub')}" ) return introspection_data elif response.status_code in (400, 401, 403): logger.warning( f"Token introspection failed: HTTP {response.status_code}. " f"Response: {response.text[:200] if response.text else 'empty'}" ) return None else: logger.warning( f"Unexpected response from introspection: {response.status_code}. " f"Response: {response.text[:200] if response.text else 'empty'}" ) return None except httpx.TimeoutException: logger.error("Timeout while introspecting token") return None except httpx.RequestError as e: logger.error(f"Network error while introspecting token: {e}") return None except Exception as e: logger.error(f"Unexpected error during token introspection: {e}") return None def _create_access_token( self, token: str, payload: dict[str, Any] ) -> AccessToken | None: """ Create AccessToken object from validated token payload. Args: token: The bearer token payload: Validated token payload Returns: AccessToken object or None if required fields missing """ # Extract username (sub claim, with fallback to preferred_username) username = payload.get("sub") or payload.get("preferred_username") if not username: logger.error( "No 'sub' or 'preferred_username' claim found in token payload" ) return None # Extract scopes from scope claim (space-separated string) scope_string = payload.get("scope", "") scopes = scope_string.split() if scope_string else [] logger.debug( f"Extracted scopes from token - scope claim: '{scope_string}' -> scopes list: {scopes}" ) # Extract expiration exp = payload.get("exp") if not exp: logger.warning("No 'exp' claim in token, using default TTL") exp = int(time.time() + self.cache_ttl) # Cache the result token_hash = hashlib.sha256(token.encode()).hexdigest() userinfo = { "sub": username, "scope": scope_string, **{k: v for k, v in payload.items() if k not in ["sub", "scope"]}, } self._token_cache[token_hash] = (userinfo, exp) return AccessToken( token=token, client_id=payload.get("client_id", ""), scopes=scopes, expires_at=exp, resource=username, # Store username in resource field (RFC 8707) ) def _get_cached_token(self, token: str) -> AccessToken | None: """ Retrieve a token from cache if not expired. Args: token: The bearer token to look up Returns: AccessToken if cached and valid, None otherwise """ token_hash = hashlib.sha256(token.encode()).hexdigest() if token_hash not in self._token_cache: return None userinfo, expiry = self._token_cache[token_hash] # Check if expired if time.time() >= expiry: logger.debug("Cached token expired, removing from cache") del self._token_cache[token_hash] return None # Return cached AccessToken username = userinfo.get("sub") or userinfo.get("preferred_username") scope_string = userinfo.get("scope", "") scopes = scope_string.split() if scope_string else [] return AccessToken( token=token, client_id=userinfo.get("client_id", ""), scopes=scopes, expires_at=int(expiry), resource=username, ) def clear_cache(self): """Clear the token cache.""" self._token_cache.clear() logger.debug("Token cache cleared") async def close(self): """Cleanup resources.""" await self.http_client.aclose() logger.debug("Unified token verifier closed")