## Summary
adds implementation of `/.pomerium/mcp/connect` method, that takes a
`redirect_url` parameter and would ensure the user goes thru required
redirects so that its session is hydrated with the upstream Oauth token
for the MCP server.
the `redirect_url` parameter host must match one of the _client_ mcp
routes (currently identified by the presence of `mcp:
pass_upstream_access_token: true` in the route.
## Related issues
Fix
https://linear.app/pomerium/issue/ENG-2321/mcp-support-handling-external-oauth-servers
## User Explanation
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## Checklist
- [x] reference any related issues
- [x] updated unit tests
- [ ] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [x] ready for review