Feature request: GitLab authentication provider

[reinhart1010]

GitLab allows users to add website links on their own profile, so it would be feasible to integrate GitLab accounts to IndieAuth.

[gRegorLove]

This came up in chat as a potential alternative to github.

Gitlab OAuth2 docs: https://docs.gitlab.com/ee/api/oauth2.html

[aaronpk]

I am not opposed to this, but it will be limited to gitlab.com. Unless gitlab opens up a public dynamic client registration endpoint I don't have a way to make it work with arbitrary gitlab instances.

In other news, I went to go register an OAuth client on gitlab.com and my account has been blocked for some reason. I am asking support about this, and will hopefully find out the reason I was blocked. I only ever used the account to comment on other projects, but I didn't have any repositories of my own. Depending on what they say, I may or may not have enough confidence that my account won't be blocked again in the future, which would break an OAuth client registered to me, so we'll see.