code: function() {
        // UI initialized, it is OK to cancel last operation.
        self.initialized_ = true;
        // retrieve is only called if auto sign-in is enabled. Otherwise, it will
        // get skipped.
        var retrieveCredential = Promise.resolve(null);
        if (!autoSignInDisabled) {
          retrieveCredential =
              self.googleyolo_.retrieve(
                  /** @type {!SmartLockRequestOptions} */ (config))
                  .catch(function(error) {
                    // For user cancellation or concurrent request pass down.
                    // Otherwise suppress and run hint.
                    if (error.type ===
                        firebaseui.auth.GoogleYolo.Error.USER_CANCELED ||
                        error.type ===
                        firebaseui.auth.GoogleYolo.Error.CONCURRENT_REQUEST) {
                      throw error;
                    }
                    // Ignore all other errors to give hint a chance to run next.
                    return null;
                  });
        }
        // Check if a credential is already available (previously signed in with).
        return retrieveCredential
            .then(function(credential) {
              if (!credential) {
                // Auto sign-in not complete.
                // Show account selector.
                return self.googleyolo_.hint(
                    /** @type {!SmartLockHintOptions} */ (config));
              }
              // Credential already available from the retrieve call. Pass it
              // through.
              return credential;
            })
            .catch(function(error) {
              // When user cancels the flow, reset the lastCancel promise and
              // resolve with false.
              if (error.type === firebaseui.auth.GoogleYolo.Error.USER_CANCELED) {
                self.lastCancel_ = Promise.resolve();
              } else if (error.type ===
                         firebaseui.auth.GoogleYolo.Error.CONCURRENT_REQUEST) {
                // Only one UI can be rendered at a time, cancel existing UI
                // and try again.
                self.cancel();
                return self.show(config, autoSignInDisabled);
              }
              // Return null as no credential is available.
              return null;
            });
      }
docs: One-Tap UI renderer.