Google Cloud BigQuery MCP connector: OAuth redirect_uri_mismatch (Error 400)

Environment

• Claude Code (CLI), macOS (Darwin 25.5.0)
• Model: Opus 4.7 (1M context)
• Connector: claude.ai Google Cloud BigQuery (claudeai-proxy → https://bigquery.googleapis.com/mcp)

Steps to reproduce

1. From an active Claude Code session, run /mcp
2. Select claude.ai Google Cloud BigQuery
3. Choose authenticate / connect
4. Browser opens to Google OAuth consent
5. Sign in with a Google Workspace account

Expected

OAuth flow completes and the connector's data tools (queries, dataset listing) become available in the session.

Actual

Google returns:

Error 400: redirect_uri_mismatch Request details: flowName=GeneralOAuthFlow

The redirect URI the connector sends is not registered on the OAuth client Google is matching against.

Notes

• The two visible tools on the connector are authenticate and complete_authentication. The authenticate tool, when called from inside a session, returns "Ask the user to run /mcp and select '…' to authenticate" — so the flow is intended to be driven entirely by the /mcp UI.
• Calling authenticate is not the failure point; the failure is on Google's side after the consent screen attempt, suggesting the connector's registered redirect URI is wrong (or scoped to a different OAuth client than the one being invoked).
• The Google_Compute_Engine connector exposes the same authenticate/complete_authentication pair — untested but likely affected if it shares the same OAuth client config.
• Gmail / Calendar / Drive connectors on the same account work fine, so it's not an account-level issue.

Workaround

None inside Claude Code. Falling back to bq CLI with gcloud ADC.