Merge commit 'c40ab43dc703be988c277d4ba6b7987a3a80e16c' into glitch-soc/merge-upstream

Conflicts:
- `app/helpers/application_helper.rb`:
  Upstream added a helper where glitch-soc had its own, not really
  a conflict.
  Added upstream's helper.
- `lib/sanitize_ext/sanitize_config.rb`:
  Upstream renamed a constant that was used slightly differently in glitch-soc.
  Renamed it as upstream did.

app/controllers/concerns/web_app_controller_concern.rb

@@ -13,7 +13,7 @@ module WebAppControllerConcern
       policy = ContentSecurityPolicy.new
 
       if policy.sso_host.present?
-        p.form_action policy.sso_host
+        p.form_action policy.sso_host, -> { "https://#{request.host}/auth/auth/" }
       else
         p.form_action :none
       end