## Summary
Adds `POST /.pomerium/mcp/routes/disconnect` that allows an MCP client
application to request upstream OAuth2 tokens to be purged, so that a
user may get a new ones with possibly different scopes.
## Related issues
Fix
https://linear.app/pomerium/issue/ENG-2545/mcp-user-should-be-able-to-purge-their-upstream-oauth2-token
## User Explanation
<!-- How would you explain this change to the user? If this
change doesn't create any user-facing changes, you can leave
this blank. If filled out, add the `docs` label -->
## Checklist
- [x] reference any related issues
- [x] updated unit tests
- [x] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [x] ready for review
## Summary
Fixes to MCP code registration and token requests.
1. ease some requirements on fields that are RECOMMENDED
2. fill in defaults
3. store both request and response in the client registration
4. check client secret in the /token request
## Related issues
- Fixes
https://linear.app/pomerium/issue/ENG-2462/mcp-ignore-unknown-grant-types-in-the-client-registration
- Fixes
https://linear.app/pomerium/issue/ENG-2461/mcp-support-client-secret-in-dynamic-client-registration
## User Explanation
<!-- How would you explain this change to the user? If this
change doesn't create any user-facing changes, you can leave
this blank. If filled out, add the `docs` label -->
## Checklist
- [x] reference any related issues
- [x] updated unit tests
- [x] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [ ] ready for review
