Django Allauth (#201)

[gdude2002]

This pull request implements Django Allauth as described in #201.

Fixes #201.

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This is a fairly big PR which, I think, may have had a little scope creep. Here's what it changes:

• Add django-allauth dependency
• Implements Discord OAuth logins using django-allauth
• Exposes messages from the Django messages framework as slide-in Bulma notifications at the top right of the page, positioned just below the navbar
• Re-styles Bulma notifications when used in the context of the Django messages framework
• Redefines Bulma's bundled colours, in order to make them less loud and make Bulma calculate colours based on the primary blurple better (by redefining turquoise to blurple)
• Implements some logic to synchronise Discord roles and Django permissions groups based on signals emitted by various events

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I would super love some reviews for this, particularly when it comes to the tests I wrote for the signal handlers, and the signal handling itself.

I'm not super happy with the signal handlers test - it's more setup than test! If anyone has any ideas on how to clean that up, I'd appreciate it.

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Old TODO:

• Set up signal listeners for Allauth events
• Set up signal listeners for relevant Model save events
• Document the signal system in comments/docstrings
• Fix up message system
  • Move messages to a corner
  • Restyle messages
    • Discord embed-style messages with the left border?
    • More muted colours? Perhaps shades of the primary blurple.
• Profile page with GH connect/disconnect and account delete
• Create templates for the Allauth-provided account pages
• Review the Allauth URLs to ensure we're only using what we need
  • Ensure login page explains the data we're collecting and collects explicit consent
• Create a user profile page (or just send them back to the homepage)
• Figure out how to signpost/link to this system from the rest of the site

[gdude2002]

Super happy to say that this PR is now ready for review! Here are some screenshots and videos that showcase the changes I've made.

Login link in dropdown

New Bulma colours, shown here as notification styles

Django admin, showing a role mapping

Django admin, showing my Discord account, sans email

MP4 showing the login flow

[jchristgit]

This looks pretty solid so I will have to resort to notpicking :(

The role mapping model is just about the cleanest way I have seen to accomplish this. I think in my last implementation of this I just hardcoded that, but a nice admin frontend for it is pretty brilliant.

That said, if the role mappings update, shouldn't the signal handler fire?

[gdude2002]

Good catch on the missing signals. I'm leaving a short TODO list in this comment so I don't forget:

• Handle RoleMapping deletions
• Handle RoleMapping updates (use pre_save and check against object already in DB if possible, otherwise try to disallow updates)

[gdude2002]

Alright, I think that's all of your review addressed, @jchristgit!

[jchristgit]

very solid work

[lemonsaurus]

Very high quality PR, but I do have a few requests before I can approve.

[scragly]

Absolutely sexy. LGTM

Comments all addressed