code: public static Response.ResponseBuilder makeCORS(Response.ResponseBuilder responseBuilder,
        String returnMethod) {
      // TODO(william): Make origin, methods, and headers configurable.
      Response.ResponseBuilder rb = responseBuilder.header("Access-Control-Allow-Origin", "*")
          .header("Access-Control-Allow-Methods", "GET, POST, OPTIONS");
  
      if (!"".equals(returnMethod)) {
        rb.header("Access-Control-Allow-Headers", returnMethod);
      }
  
      return rb;
    }
docs: Makes the responseBuilder CORS compatible.
  
  @param responseBuilder the response builder
  @param returnMethod the modified response builder
  @return response builder