User repository (#3795)

* It builds with the new user repository

* fix(test): fix broken test

* fix(api): fix registration endpoint that was broken after the change

* fix(test): update test to reflect new user repository

* fix: use interface type instead of concrete type

* fix: restore commented out code

models/auth.go

@@ -0,0 +1,11 @@
+package models
+
+// Type represents a form of authentication.
+type AuthType string
+
+// The different auth types we support.
+const (
+	// IndieAuth https://indieauth.spec.indieweb.org/.
+	IndieAuth AuthType = "indieauth"
+	Fediverse AuthType = "fediverse"
+)