authn: Load legacy plugin ID's from DB and log them.

rhodecode/authentication/__init__.py

@@ -27,6 +27,7 b' from rhodecode.authentication.registry i'
 from rhodecode.authentication.routes import root_factory
 from rhodecode.authentication.routes import AuthnRootResource
 from rhodecode.config.routing import ADMIN_PREFIX
+from rhodecode.model.settings import SettingsModel
 
 log = logging.getLogger(__name__)
 
@@ -50,6 +51,15 b' def _discover_plugins(config, entry_poin'
     return _discovered_plugins
 
 
+def _discover_legacy_plugins(config, prefix='py:'):
+    auth_plugins = SettingsModel().get_setting_by_name('auth_plugins')
+    enabled_plugins = auth_plugins.app_settings_value
+    legacy_plugins = [id_ for id_ in enabled_plugins if id_.startswith(prefix)]
+
+    log.debug('Trying to load these legacy authentication plugins {}'.format(
+        legacy_plugins))
+
+
 def includeme(config):
     # Set authentication policy.
     authn_policy = SessionAuthenticationPolicy()
@@ -83,3 +93,4 b' def includeme(config):'
 
     # Auto discover authentication plugins and include their configuration.
     _discover_plugins(config)
+    _discover_legacy_plugins(config)