title: Does Azure Push Notification support a user Id or alias?
body: <p>I am evaluating which Push Notification service to use out of Azure Mobile Services, Parse and Urban Airship.</p>
  
  <p>One of the criteria is whether the service provides a way for the app to register a bespoke user Id or alias that can then easily be used when calling the service to send a push notification to an individual. This removes the need for our backend service to have a lookup table giving us the service registration ID for a given user.</p>
  
  <p>Urban Airship has the alias feature: <a href="http://docs.urbanairship.com/connect/connect_audience.html#aliases" rel="nofollow">http://docs.urbanairship.com/connect/connect_audience.html#aliases</a> </p>
  
  <p>Parse has a sophisticated Installation object which behaves like a dictionary so that additional values can be added to it (like UserId). When the Parse service is called to send a Push Notification a query can be used to specify the user that will receive the message:
  <a href="https://www.parse.com/docs/push_guide#sending-queries/REST" rel="nofollow">https://www.parse.com/docs/push_guide#sending-queries/REST</a></p>
  
  <p>Is there an equivalent feature in Azure Mobile Services?</p>