Restrict sign ups to GitHub, work on UX

[brianlovin]

Status

• WIP
• Ready for review
• Needs testing

Deploy after merge (delete what needn't be deployed)

• api
• hyperion (frontend)

[brianlovin]

@mxstbr this is going to be hard to get right, so please poke around and help me identify where this flow is confusing.

The key changes:

• we reject new users created in the API if the providerMethod is not GitHub. If it's the case that a user is trying to create a new account with another provider, it will redirect the user to /new/user. On this view, we now render a "sign up" screen if the user is not signed in - the only option provided is GitHub. There is an escape hatch back to /login where all signup methods are available for existing users.

Please review carefully and leave feedback! We can follow up later with in-app upsells for people to connect existing non-GitHub authed accounts with a GitHub profile.

[mxstbr]

Wow I really like how this works, great work! Quick bug reports:

1. Being unauthenticated, going to a community view, then clicking "Join", and then clicking "Sign up" leads to this state, the modal does not close correctly: (also, the header text should match the button text with "Log in")

2. Am I correct in assuming this removes support for custom login screens?

Some communities are going to be a bit mad—we should link to a "FAQ" section next to this blurb that (in abstract terms) explains why signups are restricted.

[brianlovin]

@mxstbr ready for re-review. I've updated /:communitySlug/login and the login modal behavior.

[mxstbr]

LGTM!