Updating a user with the rest service

i'm trying to update a user with the rest service. I have the following user descriptor:

  <user>
    <enabled>false</enabled>
    <externallyDefined>false</externallyDefined>
    <fullName>Joe User</fullName>
    <tenantId>develdb</tenantId>
    <username>joeuser</username>
  </user>
 

Wich i'm using for a post request to the following url: http://localhost:8080/jasperserver-pro/rest/user/

But it gives a 400 Bad request code. Is this the right user descriptor to send ? I couldn't find a example of a descriptor... We are using jasperserver 4.7.

Peter