fix: enhance error handling in OAuth callback by adding connection error management and improving response validation

Author: gainsborouo

backend/app/services/auth.py

@@ -9,35 +9,44 @@ async def oauth_callback(code: str, state: str = None, stored_state: str = None)
     if not state or not stored_state or not hmac.compare_digest(state, stored_state):
         raise HTTPException(status_code=400, detail="Invalid state parameter")
 
-    async with httpx.AsyncClient() as client:
-        token_resp = await client.post(
-            settings.OAUTH_TOKEN_URL,
-            data={
-                "grant_type": "authorization_code",
-                "code": code,
-                "client_id": settings.OAUTH_CLIENT_ID,
-                "client_secret": settings.OAUTH_CLIENT_SECRET,
-                "redirect_uri": settings.OAUTH_REDIRECT_URI,
-            }
-        )
-        if token_resp.status_code != 200:
-            raise HTTPException(status_code=token_resp.status_code, detail="OAuth token exchange failed")
+    try:
+        async with httpx.AsyncClient() as client:
+            token_resp = await client.post(
+                settings.OAUTH_TOKEN_URL,
+                data={
+                    "grant_type": "authorization_code",
+                    "code": code,
+                    "client_id": settings.OAUTH_CLIENT_ID,
+                    "client_secret": settings.OAUTH_CLIENT_SECRET,
+                    "redirect_uri": settings.OAUTH_REDIRECT_URI,
+                }
+            )
+    except httpx.RequestError as e:
+        raise HTTPException(status_code=502, detail=f"Failed to connect to OAuth server: {e}")
+
+    if token_resp.status_code != 200:
+        raise HTTPException(status_code=token_resp.status_code, detail="OAuth token exchange failed")
 
-        token_data = token_resp.json()
-        access_token = token_data["access_token"]
+    token_data = token_resp.json()
+    access_token = token_data["access_token"]
+    
+    try:
+        async with httpx.AsyncClient() as client:
+            profile_resp = await client.get(
+                settings.OAUTH_USERINFO_URL,
+                headers={"Authorization": f"Bearer {access_token}"}
+            )
+    except httpx.RequestError as e:
+        raise HTTPException(status_code=502, detail=f"Failed to fetch user info: {e}")
+
+    if profile_resp.status_code != 200:
+        raise HTTPException(status_code=profile_resp.status_code, detail="Cannot fetch user info")
 
-        profile_resp = await client.get(
-            settings.OAUTH_USERINFO_URL,
-            headers={"Authorization": f"Bearer {access_token}"}
-        )
-        if profile_resp.status_code != 200:
-            raise HTTPException(status_code=profile_resp.status_code, detail="Cannot fetch user info")
-            
-        userinfo = profile_resp.json()
-        return {
-            "provider": "nycu",
-            "sub": userinfo.get("username"),
-            "email": userinfo.get("email"),
-            "name": userinfo.get("username"),
-            "avatar_url": None
-        } 
+    userinfo = profile_resp.json()
+    return {
+        "provider": "nycu",
+        "sub": userinfo.get("username"),
+        "email": userinfo.get("email"),
+        "name": userinfo.get("username"),
+        "avatar_url": None
+    }