What this does

Error handling on device code exchanges now:

• Looks at header for github rate limit info to specify how long to wait for.
• Checks forapplication/x-www-form-urlencoded header which means our requestAccept header was not checked
• If all else fails, return status code and mime type info for debugging.

This was all information we wanted when debugging the failures from github, so it's all valuable info that can be hit in prod.

Test extra

Implemented a test to show how to use the new idp device flow. Honestly in practice, the current method is easier, so using this is a bit overkill. I mainly implemented it so I can test the UI, which is much harder to mock up.

This does actually run our device auth flow in a unit test though, which has value, so I am going to keep it.

Notes

I noticed we have the UI poll for the device auth to finish, I wonder if we should just do this with a websocket on the FE, and have the BE control the rate of request.