NETCORE 3.1 solves cross domain problems

stay  Startup Class  

(1)ConfigureServices Function ：

 // Configure cross domain processing , Allow all sources
 

services.AddCors(options =>
                options.AddPolicy("all", p => p.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader())
    );

(2) Configure Function ：

 

 app.UseCors("all");

 ok , Perfect solution