HTTP Forwarder

You can customize the HTTP forwarder behavior in two ways

provide a customized HTTP client for outgoing calls
provide custom request/response transformation

Custom HTTP clients

By default, Duende.BFF will create and cache an HTTP client per configured route or local path.

This invoker is set up like this:

var client = new HttpMessageInvoker(new SocketsHttpHandler
{
    UseProxy = false,
    AllowAutoRedirect = false,
    AutomaticDecompression = DecompressionMethods.None,
    UseCookies = false
});

If you want to customize the HTTP client for specific paths, you can either implement the IHttpMessageInvokerFactory interface or derive from the DefaultHttpMessageInvokerFactory, e.g.:

public class MyInvokerFactory : DefaultHttpMessageInvokerFactory
{
    public override HttpMessageInvoker CreateClient(string localPath)
    {
        if (localPath == "/foo")
        {
            return Clients.GetOrAdd(localPath, (key) =>
            {
                return new HttpMessageInvoker(new SocketsHttpHandler
                {
                    // this API needs a proxy
                    UseProxy = true,
                    Proxy = new WebProxy("https://myproxy"),

                    AllowAutoRedirect = false,
                    AutomaticDecompression = DecompressionMethods.None,
                    UseCookies = false
                });
            });
        }

        return base.CreateClient(localPath);
    }
}

…and override our registration:

services.AddSingleton<IHttpMessageInvokerFactory, MyInvokerFactory>();

Custom Transformations

In the standard configuration, BFF uses the YARP default behavior for forwarding HTTP requests. In addition, we

remove the sensitive session cookie
add the current access token

If you want to modify this behavior you can either implement IHttpTransformerFactory from scratch:

public interface IHttpTransformerFactory
{
    /// <summary>
    /// Creates a HTTP transformer based on the local path
    /// </summary>
    /// <param name="localPath">Local path the remote API is mapped to</param>
    /// <param name="accessToken">The access token to attach to the request (if present)</param>
    /// <returns></returns>
    HttpTransformer CreateTransformer(string localPath, string accessToken = null);
}

…or derive from the DefaultHttpTransformerFactory.