Acquire Credentials for git-fetch over HTTPS

I am an OAuth client of the Github API, but I can’t find a way to acquire credentials via the API for a git-fetch via HTTPS.

I tried using the OAuth token directly, like you would a Personal Access Token, but that doesn’t seem to work.

When initially sending an authorization request, I explicitly set the scopes to user repo

https://github.com/login/oauth/authorize?client_id=<cid>&scope=user%20repo&state=89A0658F-83A9-4991-8F81-AAABA9D2B929

but when the authorization flow finishes, the returned scopes are always empty.

access_token=d1f55a&scope=&token_type=bearer

Why won’t scopes work? Is it even possible to use an OAuth token for performing a git-fetch via HTTPS? If not, why not?