code: function _setAuthHeaderFromAuthInfo(headers, authInfo) {
      if (authInfo.token) {
          headers.authorization = 'Bearer ' + authInfo.token;
      } else if (authInfo.username) {
          headers.authorization = _basicAuthHeader(authInfo.username,
              authInfo.password);
      } else if (headers.authorization) {
          delete headers.authorization;
      }
  }
docs: /*
  Set the "Authorization" HTTP header into the headers object from the given
  auth info.
  - Bearer auth if `token`.
  - Else, Basic auth if `username`.
  - Else, if the authorization key exists, then it is removed from headers.