请求被 CORS 策略阻止

Question

I am running a C# Controller locally and it is serving endpoint /api . I have a local html page with Javascript trying to fetch data from that endpoint. But I see the console with this failure.

Access to fetch at 'https://localhost:44388/api' from origin 'null' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

In my C# controller project, in the Startup.cs, I already setup this in public void ConfigureServices(IServiceCollection services)

    services.AddCors(options =>
    {
        options.AddDefaultPolicy(
            builder =>
            {
                builder.AllowAnyOrigin()
                                    .AllowAnyHeader()
                                    .AllowAnyMethod();
            });
    }); 

and in public void Configure(IApplicationBuilder app, IWebHostEnvironment env) , I have put

    app.UseCors(builder =>
    {
        builder
        .AllowAnyOrigin()
        .AllowAnyMethod()
        .AllowAnyHeader();
    });

Can you please tell me what am I missing?

Thank you.

Answer 1

Try to use this syntax

public void ConfigureServices(IServiceCollection services)
        {
            services.AddCors(o => o.AddPolicy("AllowAnyOrigin",
                      builder =>
                       {
                       builder.AllowAnyOrigin()
                              .AllowAnyMethod()
                              .AllowAnyHeader();
              }));

        .....
            
        }

        
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            .....

           // app.UseRouting();

            app.UseCors("AllowAnyOrigin");

         //  app.UseAuthorization();
         // app.UseEndpoints(..
 
         }

Make sure that UseCors should be in the end of Configure method but before UseAuthorizaton. AddCors should be at the top of Configure services.