Dev helper for establishing SSL connections to localhost on various platforms

DevHttpsConnectionHelper.cs

using System.Net.Security;

public class DevHttpsConnectionHelper
{
    public DevHttpsConnectionHelper(int sslPort)
    {
        SslPort = sslPort;
        DevServerRootUrl = FormattableString.Invariant($"https://{DevServerName}:{SslPort}");
        LazyHttpClient = new Lazy<HttpClient>(() => new HttpClient(GetPlatformMessageHandler()));
    }

    public int SslPort { get; }

    public string DevServerName =>
#if WINDOWS
        "localhost";
#elif ANDROID
        "10.0.2.2";
#else
        throw new PlatformNotSupportedException("Only Windows and Android currently supported.");
#endif

    public string DevServerRootUrl { get; }

    private Lazy<HttpClient> LazyHttpClient;
    public HttpClient HttpClient => LazyHttpClient.Value;

    public HttpMessageHandler? GetPlatformMessageHandler()
    {
#if WINDOWS
        return null;
#elif ANDROID
        var handler = new CustomAndroidMessageHandler();
        handler.ServerCertificateCustomValidationCallback = (message, cert, chain, errors) =>
        {
            if (cert != null && cert.Issuer.Equals("CN=localhost"))
                return true;
            return errors == SslPolicyErrors.None;
        };
        return handler;

#else
        throw new PlatformNotSupportedException("Only Windows and Android currently supported.");
#endif
    }

#if ANDROID
    internal sealed class CustomAndroidMessageHandler : Xamarin.Android.Net.AndroidMessageHandler
    {
        protected override Javax.Net.Ssl.IHostnameVerifier GetSSLHostnameVerifier(Javax.Net.Ssl.HttpsURLConnection connection)
            => new CustomHostnameVerifier();

        private sealed class CustomHostnameVerifier : Java.Lang.Object, Javax.Net.Ssl.IHostnameVerifier
        {
            public bool Verify(string? hostname, Javax.Net.Ssl.ISSLSession? session)
            {
                return
                    Javax.Net.Ssl.HttpsURLConnection.DefaultHostnameVerifier.Verify(hostname, session)
                    || hostname == "10.0.2.2" && session.PeerPrincipal?.Name == "CN=localhost";
            }
        }
    }
#endif
}

FYI since xamarin/xamarin-android#7246 was merged, the CustomHostnameVerifier hack won't be necessary in .NET 7 on Android.

@simonrozsival ah I'll have to try this again and see what works!

This works for me!

Thank you so much for sharing this!

Thanks!!!you are the best!