Cross domain problems in the configuration of.Net core version 3.1

1、Startup Content

public class Startup
    {
    
        public Startup(IConfiguration configuration)
        {
    
            Configuration = configuration;
        }

        public IConfiguration Configuration {
     get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
    
            // Configure cross domain processing , Allow all sources           
            services.AddCors(options =>
            {
    
                options.AddPolicy("cors", builder =>
                {
    
                    builder.AllowAnyOrigin() // Allow host access from any source 
                    .AllowAnyMethod()
                    .AllowAnyHeader();
                    //.AllowCredentials();// Specify treatment cookie
                });
            });
            // Cross domain configuration end

            services.AddControllers();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
    
           
            if (env.IsDevelopment())
            {
    
                app.UseDeveloperExceptionPage();
            }
            app.UseHttpsRedirection();

            app.UseRouting();

            // Allow all cross domains ,cors Is in ConfigureServices Method 
            // Be careful ：UseCors Must be on UseRouting and UseEndpoints Between 
            app.UseCors("cors");

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
    
                endpoints.MapControllers();
                // Cross domain needs to be added RequireCors Method ,cors Is in ConfigureServices Method 
                endpoints.MapControllers().RequireCors("cors");
            });


           
        }
    }

2、 Detailed instructions ,ConfigureServices To configure

 // Configure cross domain processing , Allow all sources           
            services.AddCors(options =>
            {
    
                options.AddPolicy("cors", builder =>
                {
    
                    builder.AllowAnyOrigin() // Allow host access from any source 
                    .AllowAnyMethod()
                    .AllowAnyHeader();
                    //.AllowCredentials();// Specify treatment cookie
                });
            });

3、Configure To configure

 // Allow all cross domains ,cors Is in ConfigureServices Method 
            // Be careful ：UseCors Must be on UseRouting and UseEndpoints Between 
            app.UseCors("cors");

// Cross domain needs to be added RequireCors Method ,cors Is in ConfigureServices Method 
                endpoints.MapControllers().RequireCors("cors");

4、 Be careful
（1） UseCors Must be on UseRouting and UseEndpoints Between , Particular attention , Order matters
（2）.net core 2.2 and 3.1 Version cross domain configuration is different
Use 2.2 Version method configuration , stay 3.1 The version will appear Not all cross domain

5、 see .net core 2.2 Version cross domain configuration

6、.net Cross domain method configuration official document , You can have a look at what you need Click to see