I want to avoid falling back to the old OAuth flow for just any HTTP
4xx/5xx because other statuses should be allowed to surface a problem
with a request or the server.
Before, we implemented the OAuth app authorization flow which requires a
callback URL. To provide such a URL, we had to spin up a local HTTP
server, which was brittle and did not cover cases where a person might
want to authenticate with a browser that runs on a different machine
than the GitHub CLI process.
This implements the OAuth Device Authorization flow where the user is
given a one-time code and asked to paste it in the browser flow. There
is no callback URL, so we can avoid spinning up a local server, and the
user may open a browser on any of their devices, as long as they provide
the correct one-time code.
If the Device Authorization flow is detected to be unavailable for the
OAuth app (right now, it's specifically enabled for GitHub CLI) or for
an older GitHub Enterprise instance, this falls back to the old app
authentication flow.
This ensures that while having git remotes to point to either
`github.com` or authenticated GHE instances, adding another git remote
pointing to an unrelated host won't change the remote resolution in any
way, even if the unrelated remote is called `upstream` or `github` (and
thus normally took precedence).
Accept the "HOST/OWNER/REPO" syntax or passing a full URL for both the
`--repo` flag and the GH_REPO environment variable and allow setting
GH_HOST environment variable to override just the hostname for
operations that assume "github.com" by default.
Examples:
$ gh repo clone example.org/owner/repo
$ GH_HOST=example.org gh repo clone repo
$ GH_HOST=example.org gh api user
$ GH_HOST=example.org gh gist create myfile.txt
$ gh issue list -R example.org/owner/repo
$ gh issue list -R https://example.org/owner/repo.git
$ GH_REPO=example.org/owner/repo gh issue list
