MCP Google Drive OAuth flow redirects to claude.ai web instead of completing in CLI

Description

When authenticating the claude.ai Google Drive MCP server from Claude Code CLI, the OAuth flow redirects to https://claude.ai/settings/mcp/auth_done?authed_mcp_server_id=... instead of a localhost callback URL that the CLI can capture.

Steps to Reproduce

1. In Claude Code CLI, trigger Google Drive MCP authentication (e.g., try to read a Google Doc)
2. The mcp__claude_ai_Google_Drive__authenticate tool tells the user to run /mcp and select "claude.ai Google Drive"
3. User runs /mcp, selects Google Drive, completes OAuth in browser
4. Browser redirects to https://claude.ai/settings/mcp/auth_done?authed_mcp_server_id=<id> — a web app page, not a localhost callback
5. CLI never receives the auth callback

Expected Behavior

The OAuth flow should redirect to a localhost:<port>/callback?code=...&state=... URL so the CLI can complete the flow via complete_authentication. Alternatively, the /mcp OAuth flow in CLI should handle the token exchange directly.

Actual Behavior

• authenticate tool says to run /mcp — no OAuth URL is provided directly
• /mcp completes OAuth on the web side but the CLI has no record of the flow
• complete_authentication fails with "No OAuth flow is in progress"
• Google Drive MCP tools remain unavailable in the CLI session

Environment

• Claude Code CLI (macOS, Darwin 24.6.0)
• Model: Claude Opus 4.6 (1M context)
• MCP server: claude.ai Google Drive (claudeai-proxy at https://drivemcp.googleapis.com/mcp/v1)