Add setting to allow MLC registration only (#1259)

* Adds a setting to registration visibility to allow for MLC registration while registration is disabled

CTFd/auth.py

@@ -11,6 +11,7 @@ from CTFd.utils import config, email, get_app_config, get_config
 from CTFd.utils import user as current_user
 from CTFd.utils import validators
 from CTFd.utils.config import is_teams_mode
+from CTFd.utils.config.integrations import mlc_registration
 from CTFd.utils.config.visibility import registration_visible
 from CTFd.utils.crypto import verify_password
 from CTFd.utils.decorators import ratelimit
@@ -384,7 +385,7 @@ def oauth_redirect():
             user = Users.query.filter_by(email=user_email).first()
             if user is None:
                 # Check if we are allowing registration before creating users
-                if registration_visible():
+                if registration_visible() or mlc_registration():
                     user = Users(
                         name=user_name,
                         email=user_email,