Add support for grpc.ssl_target_name_override

[jayd16]

I would like to see support for for the grpc.ssl_target_name_override ChannelOption from the legacy Grpc.Core implementation supported in grpc-dotnet. This is a very nice testing feature.

I can't find the equivalent configuration in grpc-dotnet. I've also tried setting the request host header from HttpClientHandler by overriding SendAsync and that doesn't seem to work.

I cannot simply ignore the server certificate from the client either. The ServerCertificateCustomValidationCallback is never even hit because the Grpc server will only return a cert for the requested host and otherwise kill the socket. An example of the server error when requesting the wrong host:
E0805 18:58:05.678826 123145379745792 /tmpfs/src/github/grpc/workspace_csharp_ext_macos_x64/src/core/tsi/ssl_transport_security.cc:1837: No match found for server name: localhost.

Can this be added or is there some other way to achieve this? Thanks!

[JamesNK]

I think this would need to be supported in SocketsHttpHandler first. Grpc.Net.Client uses it for its networking layer.

[jayd16]

If that's the case, there might already be a way? SocketsHttpHandler.SslOptions.TargetHost.

Is there a way to get at this configuration already?

[JamesNK]

Create SocketsHttpHandler, configure it how you want, then pass it to gRPC channel using GrpcChannelOptions.HttpHandler property.

[jayd16]

Hmm I'm using Unity's new .net standard 2.1 support which uses the older HttpClientHandler.

There also seem to be Unity related issues. I confirmed that customizing the HttpClientHandler.ServerCertificateCustomValidationCallback works fine in a normal .net5.0 app.

I'll close this ticket and move the discussion to #1309.