For GitHub this returns the App install URL carrying a signed, short-lived
state token that binds the install back to the authenticated caller. The
caller redirects the user there; GitHub completes the install with a
callback to a route this contract does not publish, since it is invoked by
GitHub’s own installation flow rather than by your client. An unsupported
provider is rejected with 422, naming the supported providers.
This route requires the write scope.A missing or invalid credential returns 401 authentication_error. A valid credential without the scope returns 403 permission_denied, and the problem body names the exact scope required.