code: private static Node checkPosterIdentifier(final HttpServletRequest request,
  			final ReadResponse response) {
  		final String posterId = request
  				.getParameter(ProtocolConstants.Parameters.Read.POSTER_IDENTIFIER);
  		if (posterId != null) {
  			final Node user = NeoUtils.getUserByIdentifier(posterId);
  			if (user != null) {
  				return user;
  			}
  			response.posterIdentifierInvalid(posterId);
  		} else {
  			response.posterIdentifierMissing();
  		}
  
  		return null;
  	}
docs: check if the request contains a valid poster identifier
  
  @param request
  Tomcat servlet request
  @param response
  response object
  @return user node with the identifier passed<br>
  <b>null</b> if the identifier is invalid