JSON Listing contains invalid data

[at88mph]

As per JSON.org, numbers may not begin with a zero, but when listing users, some IDs begin with a zero, but are written out as a number datatype.

To reproduce within CADC:

Authenticated request to /ac/users/ with the Accept: application/json header set.
First returned value has identities/$/@type=HTTP numeric value that begins with zero.
The JSON parser in the browser fails to load this, and so we cannot make a proper CORS request.

The username, in this case, needs to be declared as a String.