Warning log msg when http basic auth fails

actions/api.php

@@ -67,6 +67,7 @@ class ApiAction extends Action
                     $this->process_command();
                 } else {
                     # basic authentication failed
+                    common_log(LOG_WARNING, "Failed API auth attempt, nickname: $nickname.");
                     $this->show_basic_auth_error();
                 }
             }