[LS] Support OAuth authentication on self-managed instances

Problem to solve

The extension provides a simple way to authenticate to GitLab.com using OAuth.

But for self managed, the extension only supports personal access token (PAT) authentication.

Proposal

Allow users to configure supported OAuth instances. This will require changing the current behaviour which is hardcoding https://gitlab.com and the OAuth client ID in the authentication provider

The result for user would look like this:

1. Set up an OAuth app in the GitLab instance https://docs.gitlab.com/ee/integration/oauth_provider.html
2. add setting.json properties gitlab.oauthConfig = [{instanceUrl, clientID})
3. after that, the OAuth login would work for their instanceUrl

original description with use case from the Drupal Team

Problem to solve

Drupal, a popular PHP CMS framework, is using https://git.drupalcode.org/ to manage issues for it core, contributed and custom modules. Unforunately, the current implementation does not implement personal access tokens. This means that this extension can not authenticate with it.

There is an open issue, Drupal Issue 3199831, to address this but there has not had meaningful movement in 2+ years.

Proposal

It would be great if this site supported SSO login on non-gitlab.com domains.

Further details

I understand that authentication is hard. There are security implications and stakeholders to manage. Please feel free to dismiss this if it out-of-scope for the extension goals and roadmap.

Regardless, thank you for the work on the extension. It improves my workflow when using gitlab.com. 😃

Links / references

Drupal Issue 3199831