Request metadata brainstorm

- Client IP and port
- Local IP and port
- TLS metadata
  - Client certificate (what is the object format here)
  - TLS or DTLS
  - Cipher
- HTTP protocol (h1 vs h2 vs h3)
- Vendor specific extensions
  - Geolocation? 


Things in `Request`:
- url
- method
- headers
  - many frameworks have helpers to parse these: content negotiation
- body (and body length)
