In ASP.NET Core 6, you can handle CORS (Cross-Origin Resource Sharing) and specify the allowed origins using the AddCors method in the Startup.cs file. Here's a simple example:

Open your Startup.cs file.

In the ConfigureServices method, add the following code to configure CORS:

public void ConfigureServices(IServiceCollection services)
{
    // Other service configurations

    services.AddCors(options =>
    {
        options.AddPolicy("AllowSpecificOrigin", builder =>
        {
            builder.WithOrigins("https://yourallowedorigin.com")
                   .AllowAnyHeader()
                   .AllowAnyMethod();
        });
    });

    // More service configurations
}

Replace "https://yourallowedorigin.com" with the actual origin you want to allow.

1. In the Configure method, add the following code to use the CORS policy:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    // Other app configurations

    app.UseCors("AllowSpecificOrigin");

    // More app configurations
}

This will allow requests from the specified origin. Adjust the configuration according to your specific needs.

Remember to replace the placeholder with your actual domain, and you can customize other CORS settings as needed.