Create Slack Login/registration OAuth handler

[ksmacleod99]

Feature request

We would like to provide users the ability to register and log in using Slack.

Proposed solution

Integrate OAuth handlers on the back end to allow the user to register and log in using Slack.

Additional context

Slack OAuth documentation

[kylemh]

Auth0 integration can be covered by this ticket too, Allen 🥰

[avats-dev]

Hey, I want to work on this. Can anyone guide me how I can do this? Thanks 🎉

[kylemh]

We won't be doing this actually.