在Startup.ConfigureServices中，添加服务

注意：.net Core 3.1版本  Cors配置不能同时启用  AllowAnyOrigin()  .AllowAnyMethod()  .AllowAnyHeader()  .AllowCredentials()

否则报错 System.InvalidOperationException
  HResult=0x80131509
  Message=The CORS protocol does not allow specifying a wildcard (any) origin and credentials at the same time. Configure the CORS policy by listing individual origins if credentials needs to be supported.

Source=Microsoft.AspNetCore.Cors 

解决方法：

Configure中添加：

//启动跨域
app.UseCors(“any”);

app.UseEndpoints(endpoints =>
{
endpoints.MapControllers().RequireCors(“any”);
});

ConfigureServices中添加：

//添加跨域支持
services.AddCors(options =>
{
options.AddPolicy(“any”, builder =>
{
builder.WithMethods(“GET”, “POST”, “HEAD”, “PUT”, “DELETE”, “OPTIONS”)
//.AllowCredentials()//指定处理cookie
.AllowAnyOrigin(); //允许任何来源的主机访问
});
});