auth: optimized logging with lazy eval of params formatting

rhodecode/authentication/__init__.py

@@ -47,6 +47,7 b' def discover_legacy_plugins(config, pref'
     setting in database which are using the specified prefix. Normally 'py:' is
     used for the legacy plugins.
     """
+
     log.debug('authentication: running legacy plugin discovery for prefix %s',
               legacy_plugin_prefix)
     try:
@@ -64,10 +65,11 b' def discover_legacy_plugins(config, pref'
         except Exception as e:
             log.exception(
                 'Exception while loading legacy authentication plugin '
-                '"{}": {}'.format(plugin_id, e.message))
+                '"%s": %s', plugin_id, e)
 
 
 def includeme(config):
+
     # Set authentication policy.
     authn_policy = SessionAuthenticationPolicy()
     config.set_authentication_policy(authn_policy)