title: Using push() method to create new child location without unique key
body: <p>In my firebase web app when new users signup with their email i create a node under their email adress under the root ref</p>
  
  <p>But the problem is  using push() method to add every new user to the database every user is created with a unique key like below</p>
  
  <p>-<strong>users</strong></p>
  
  <p>----<strong>ASFTU578FE</strong></p>
  
  <p>---------user: user1@email.com</p>
  
  <p>----<strong>FDWWE36S46</strong></p>
  
  <p>---------user: user2@email.com</p>
  
  <p>----<strong>WERSRTT23W</strong></p>
  
  <p>---------user: user3@email.com</p>
  
  <p>Now how can i access the path for a user since i dont know the unque key that will be created for every new user</p>
  
  <p>Is there a way to push new user without a unique key but the key i know like user.displayName or user.email</p>