Add /auth/verify endpoint for L1 token verification

L1 servers call this endpoint to verify tokens during auth callback.
Returns user info if token is valid, 401 if invalid or revoked.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/routers/auth.py

@@ -1,14 +1,15 @@
 """
 Authentication routes for L2 server.
 
-Handles login, registration, and logout.
+Handles login, registration, logout, and token verification.
 """
 
 import hashlib
 from datetime import datetime, timezone
 
-from fastapi import APIRouter, Request, Form
+from fastapi import APIRouter, Request, Form, HTTPException, Depends
 from fastapi.responses import HTMLResponse, RedirectResponse
+from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials
 
 from artdag_common import render
 from artdag_common.middleware import wants_html
@@ -17,6 +18,7 @@ from ..config import settings
 from ..dependencies import get_templates, get_user_from_cookie
 
 router = APIRouter()
+security = HTTPBearer(auto_error=False)
 
 
 @router.get("/login", response_class=HTMLResponse)
@@ -173,3 +175,49 @@ async def logout(request: Request):
     response = RedirectResponse(url="/", status_code=302)
     response.delete_cookie("auth_token")
     return response
+
+
+@router.get("/verify")
+async def verify_token(
+    request: Request,
+    credentials: HTTPAuthorizationCredentials = Depends(security),
+):
+    """
+    Verify a token is valid.
+
+    Called by L1 servers to verify tokens during auth callback.
+    Returns user info if valid, 401 if not.
+    """
+    import db
+    from auth import verify_token as verify_jwt, get_token_claims
+
+    # Get token from Authorization header or query param
+    token = None
+    if credentials:
+        token = credentials.credentials
+    else:
+        # Try Authorization header manually (for clients that don't use Bearer format)
+        auth_header = request.headers.get("Authorization", "")
+        if auth_header.startswith("Bearer "):
+            token = auth_header[7:]
+
+    if not token:
+        raise HTTPException(401, "No token provided")
+
+    # Verify JWT signature and expiry
+    username = verify_jwt(token)
+    if not username:
+        raise HTTPException(401, "Invalid or expired token")
+
+    # Check if token is revoked
+    claims = get_token_claims(token)
+    if claims:
+        token_hash = hashlib.sha256(token.encode()).hexdigest()
+        if await db.is_token_revoked(token_hash):
+            raise HTTPException(401, "Token has been revoked")
+
+    return {
+        "valid": True,
+        "username": username,
+        "claims": claims,
+    }