code: private String checkRequestMethod(HttpServletRequest request, JCorsConfig config) {
  
  		String requestMethod = request.getHeader(CorsHeaders.ACCESS_CONTROL_REQUEST_METHOD_HEADER);
  		Constraint.ensureNotEmpty(requestMethod, "Request Method Header must be supplied");
  
  		Constraint.ensureTrue(config.isMethodAllowed(requestMethod),
  				String.format("The specified method is not allowed: '%s'", requestMethod));
  
  		return requestMethod;
  	}
docs: Checks if the requested method is allowed
  
  @param request
  @param config