## 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
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## Checklist
- [x] reference any related issues
- [x] updated unit tests
- [x] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [ ] ready for review