Oauth grant_type=password is inaccessible

[jonjohnsonjr]

Before #628 we would fall back to the oauth flow for username/password if the token flow failed. This is not great behavior, since it almost always will fail, so we removed that fallback. As a result, there's actually no way to use username/password with the oauth flow.

Docker has a similar codepath that is reachable if the ForceOAuth option is set in their TokenHandlerOptions, but as far as I can tell there's no existing code that actually exercises that path in the docker client.

It's unclear to me if any registries support this or any clients need it, and there's no easy way to tell if we should take that path from the registry response.

[github-actions]

This issue is stale because it has been open for 90 days with no
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[splucs]

/reopen

[splucs]

/remove-lifecycle stale

[splucs]

@jonjohnsonjr friendly ping on the PR for this: #1740

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Keep fresh with the 'lifecycle/frozen' label.