Add User API Problem

Given API to Add User :
@POST
@Path(value="/")
public UserDTO add(@QueryParam(value="sid")
String sid,
@FormParam(value="user")
UserDTO user,
@FormParam(value="confirm")
Boolean confirm)

URL: /user?sid="+sid

Problem in API Call : In UserDTO, External id and External type are unknown values.
How to set the External Id and External Type for the User.