fix: update auth_callback to include client_id in request body for OIDC providers

backend/app/main.py

@@ -78,15 +78,13 @@ async def auth_callback(payload: AuthCallbackRequest):
         "code": payload.code,
         "code_verifier": payload.code_verifier,
         "redirect_uri": str(payload.redirect_uri),
+        "client_id": settings.oidc_client_id,
     }
 
     # Some OIDC providers expect client credentials via HTTP Basic auth
     auth = None
     if settings.oidc_client_secret:
         auth = (settings.oidc_client_id, settings.oidc_client_secret)
-    else:
-        # public client: include client_id in the request body
-        data["client_id"] = settings.oidc_client_id
 
     async with httpx.AsyncClient(timeout=15.0) as client:
         response = await client.post(token_endpoint, data=data, headers={"Accept": "application/json"}, auth=auth)