MSC4341: Support for RFC 8628 Device Authorization Grant

[hughns]

Rendered

This was originally part of MSC4108 but has been split out to make review easier and is useful in its own right.

Implementations:

• Server
  • matrix-authentication-service: supports the device authorization grant
• Client
  • matrix-rust-sdk as a client acting as a new device wishing to log in. Code is mostly within https://github.com/matrix-org/matrix-rust-sdk/blob/main/crates/matrix-sdk/src/authentication/oauth/mod.rs
  • Test CLI in MAS: https://github.com/element-hq/matrix-authentication-service/blob/main/misc/device-code-grant.sh
  • Tutorial: https://areweoidcyet.com/client-implementation-guide/device-code-grant/