AWS - 已被 CORS 策略阻止：请求的资源上不存在“Access-Control-Allow-Origin”header

Question

I used visual studio net 2.1 and a local sql database for my site on AWS. The first page comes up but when I try to put in a comment and the code routes to another page on my site I get this console error and the page is not routed to in the browser:

Access to XMLHttpRequest at 'https...' from origin 'https://www.....dev' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

This is the startup.cs file

            services.AddCors(options =>
            {
                options.AddPolicy("CorsPolicy",
                    builder => builder.AllowAnyOrigin()
                        .AllowAnyMethod()
                        .AllowAnyHeader()
                       );
            });

           app.UseCors("CorsPolicy");

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });

Answer 1

For some CORS requests, the browser sends an additional OPTIONS request before making the actual request. This request is called a preflight request. The browser can skip the preflight request if all the following conditions are true:

1. The request method is GET, HEAD, or POST.
2. The app doesn't set request headers other than Accept, Accept-Language, Content- Language, Content-Type, or Last-Event-ID.
3. The Content-Type header, if set, has one of the following values: application/x-www-form-urlencoded multipart/form-data text/plain

AllowAnyOrigin affects preflight requests and the Access-Control-Allow-Origin header.

The preflight request uses the HTTP OPTIONS method. It may include the following headers:

Access-Control-Request-Method: The HTTP method that will be used for the actual request. Access-Control-Request-Headers: A list of request headers that the app sets on the actual request. Access-Control-Allow-Methods

Try allowing specific origins, methods and headers. For more information can check the below link:

https://docs.microsoft.com/en-us/aspnet/core/security/cors?view=aspnetcore-3.1#preflight-requests

Answer 2

THe answer is to enable the api-gateway in AWS

In API Gateway Console click the Actions dropdown and select Deploy API.

This eliminated the CORS issue.