Need a method of determining if a User email address is already used

http://docs.jboss.org/picketlink/2/latest/reference/html/ch05.html#d5e1005

according to the docs here, email address can be provided as part of the default user object, but there is no way of querying whether or not the email address is already taken, using the picketlink API. This can of course be done with the entitymanager, but it would make sense to be able to look up the user by their email address as well.

This is important because an important validation criteria when creating a new account is typically, "Email address is not used by another account."

If not adding an API, at least an example of showing how this would be done would be good.