[bigquery-maps-mcp] Bug: `adk web` returns 403 Forbidden when accessed via Cloud Shell Web Preview

[JannetEkka]

Codelab : Build a Location Intelligence ADK Agent with MCP servers for BigQuery and Google Maps

Step affected

Step 7 — "Chat with your agent!"

Description

When running adk web in Google Cloud Shell and accessing the UI via Web Preview (port 8000), the ADK web server returns a 403 Forbidden error on session creation:

POST /apps/mcp_bakery_app/users/user/sessions HTTP/1.1" 403 Forbidden

This is caused by Cloud Shell proxying requests through a *.cloudshell.dev domain, which ADK's default CORS/origin check blocks.

Fix

The codelab should instruct users to run adk web with the --allow_origins flag:

adk web --allow_origins "regex:https://.*\.cloudshell\.dev"

Steps to reproduce

1. Follow the codelab in Google Cloud Shell
2. Run adk web as instructed
3. Open the UI via Web Preview → port 8000
4. Observe 403 on session creation — the chat interface does not load

Expected behavior

The codelab should include the --allow_origins flag in the adk web command, or add a note explaining this is required when using Cloud Shell Web Preview.

[jeffonelson]

Hey @JannetEkka - thanks for the bug.

We fixed this earlier today in google/mcp#34. You should now see the command adk web --allow_origins 'regex:https://.*\.cloudshell\.dev' in Step 7 of the Codelab

Please reach out if this does not solve things.