Fediverse-based authentication (#1846)

* Able to authenticate user against IndieAuth. For #1273

* WIP server indieauth endpoint. For https://github.com/owncast/owncast/issues/1272

* Add migration to remove access tokens from user

* Add authenticated bool to user for display purposes

* Add indieauth modal and auth flair to display names. For #1273

* Validate URLs and display errors

* Renames, cleanups

* Handle relative auth endpoint paths. Add error handling for missing redirects.

* Disallow using display names in use by registered users. Closes #1810

* Verify code verifier via code challenge on callback

* Use relative path to authorization_endpoint

* Post-rebase fixes

* Use a timestamp instead of a bool for authenticated

* Propertly handle and display error in modal

* Use auth'ed timestamp to derive authenticated flag to display in chat

* Fediverse chat auth via OTP

* Increase validity time just in case

* Add fediverse auth into auth modal

* Text, validation, cleanup updates for fedi auth

* Fix typo

* Remove unused images

* Remove unused file

* Add chat display name to auth modal text

auth/auth.go

@@ -4,8 +4,8 @@ package auth
 type Type string
 
 // The different auth types we support.
-// Currently only IndieAuth.
 const (
 	// IndieAuth https://indieauth.spec.indieweb.org/.
 	IndieAuth Type = "indieauth"
+	Fediverse Type = "fediverse"
 )