setup fastapi auth using authentik instance

crawler/api/auth.py

@@ -0,0 +1,64 @@
+from datetime import timedelta
+from api.config import AUTHENTIK_URL, OIDC_CACHE_TTL, OIDC_CLIENT_ID, OIDC_METADATA_URL
+from cachetools import TTLCache
+from fastapi import Depends, HTTPException
+from fastapi.security import OAuth2AuthorizationCodeBearer
+from httpx import AsyncClient
+import jwt
+from pydantic import BaseModel
+
+
+# OAuth2 Scheme
+oauth2_scheme = OAuth2AuthorizationCodeBearer(
+    authorizationUrl=f"{AUTHENTIK_URL}/application/o/authorize/",
+    tokenUrl=f"{AUTHENTIK_URL}/application/o/token/",
+)
+
+JWKS_CACHE = TTLCache(maxsize=1, ttl=OIDC_CACHE_TTL)
+OIDC_METADATA_CACHE = TTLCache(maxsize=1, ttl=OIDC_CACHE_TTL)
+
+
+class User(BaseModel):
+    sub: str  # User ID
+    email: str
+    name: str
+
+
+async def get_oidc_metadata():
+    if "oidc_metadata" not in OIDC_METADATA_CACHE:
+        async with AsyncClient() as client:
+            resp = await client.get(OIDC_METADATA_URL, follow_redirects=True)
+        OIDC_METADATA_CACHE["oidc_metadata"] = resp.json()
+    return OIDC_METADATA_CACHE["oidc_metadata"]
+
+
+async def get_cached_jwks_client() -> jwt.PyJWKClient:
+    if "jwks_client" not in JWKS_CACHE:
+        metadata = await get_oidc_metadata()
+        jwks_url = metadata["jwks_uri"]
+        JWKS_CACHE["jwks_client"] = jwt.PyJWKClient(
+            jwks_url,
+            cache_keys=True,  # PyJWT's built-in key caching
+            max_cached_keys=5,
+        )
+    return JWKS_CACHE["jwks_client"]
+
+
+async def get_current_user(token: str = Depends(oauth2_scheme)) -> User:
+    try:
+        # Fetch JWKS keys from Authentik
+        metadata = await get_oidc_metadata()
+        signing_key = (await get_cached_jwks_client()).get_signing_key_from_jwt(token)
+
+        # Decode and verify JWT
+        payload = jwt.decode(
+            token,
+            signing_key,
+            algorithms=["RS256"],
+            audience=OIDC_CLIENT_ID,
+            issuer=metadata["issuer"],
+            options={"verify_exp": False},
+        )
+        return User(**payload)
+    except jwt.PyJWTError as e:
+        raise HTTPException(status_code=401, detail=f"Invalid token: {e}")