title: gmail API watch webhook: how to get the user-id
body: <p>We need to use push notifications for many users, using watch Gmail API call. </p>
  
  <p>The watch response we should get on the webhook does not contain any information about the user for which the webhook has been called.</p>
  
  <p>The problem is that according to <a href="https://developers.google.com/gmail/api/v1/reference/users/history/list" rel="nofollow noreferrer">Users.history: list</a>
  I cannot get messages without user-id.</p>
  
  <p>How am I supposed to get user-id from the watch webhook?
  OR
  Is it possible to call something similar to "Users.history: list" without the need to have user-id?</p>
  
  <p>Thanks for your support,
  Adrien </p>