backend: add FastAPI scaffold, models, oauth flow, schema

modern/backend/oauth.py

@@ -0,0 +1,39 @@
+import os
+from fastapi import APIRouter, Request
+from starlette.responses import RedirectResponse
+from authlib.integrations.starlette_client import OAuth
+
+router = APIRouter()
+
+oauth = OAuth()
+
+# Register provider with placeholders; read from env at runtime
+GOOGLE_CLIENT_ID = os.getenv('GOOGLE_CLIENT_ID')
+GOOGLE_CLIENT_SECRET = os.getenv('GOOGLE_CLIENT_SECRET')
+BASE_URL = os.getenv('BASE_URL', 'http://localhost:8000')
+
+if GOOGLE_CLIENT_ID and GOOGLE_CLIENT_SECRET:
+    oauth.register(
+        name='google',
+        client_id=GOOGLE_CLIENT_ID,
+        client_secret=GOOGLE_CLIENT_SECRET,
+        server_metadata_url='https://accounts.google.com/.well-known/openid-configuration',
+        client_kwargs={'scope': 'openid email profile https://www.googleapis.com/auth/calendar.events'}
+    )
+
+@router.get('/oauth/google/login')
+async def google_login(request: Request):
+    if 'google' not in oauth:
+        return {'error': 'google oauth not configured; set GOOGLE_CLIENT_ID and GOOGLE_CLIENT_SECRET'}
+    redirect_uri = BASE_URL + '/api/v1/oauth/google/callback'
+    return await oauth.google.authorize_redirect(request, redirect_uri)
+
+@router.get('/oauth/google/callback')
+async def google_callback(request: Request):
+    if 'google' not in oauth:
+        return {'error': 'google oauth not configured'}
+    token = await oauth.google.authorize_access_token(request)
+    user = await oauth.google.parse_id_token(request, token)
+    # token contains access_token and refresh_token; persist securely
+    # For demo, return token info
+    return {'token': token, 'user': user}