code: @POST
    @Path("me/username")
    @RolesAllowed({"ROLE_ADMIN", "ROLE_USER"})
    public Response changeUsername(@Context HttpServletRequest request, UsernameRequest usernameRequest) {
      Long userId = (Long) request.getAttribute(OAuth2Filter.NAME_USER_ID);
      return changeUsername(userId, usernameRequest);
    }
docs: Change current users username.
  The username must be unique
  
  @param usernameRequest new username
  @return 200 if success
  409 if username is not unique