Feature request: Improve gRPC client Certificate handling

It would help, if it was possible to use a pfx file with password, or a thumbprint from the client. This would make it easy to setup HTTPS with the client for different deployment types.

something like this:

example 1:

cert = new X509Certificate2(Path.Combine(_environment.ContentRootPath, "sts_dev_cert.pfx"), "1234");

example 2:

using (X509Store store = new X509Store(StoreName.My, StoreLocation.LocalMachine))
{
  store.Open(OpenFlags.ReadOnly);
  var certs = store.Certificates.Find(X509FindType.FindByThumbprint, certificateThumbprint, false);
  cert = certs[0];
  store.Close();
}

example 3:

var vaultConfigSection = Configuration.GetSection("Vault");
var keyVaultService = new KeyVaultCertificateService(vaultConfigSection["Url"], vaultConfigSection["ClientId"], vaultConfigSection["ClientSecret"]);
cert = keyVaultService.GetCertificateFromKeyVault(vaultConfigSection["CertificateName"]);

[JamesNK]

Raise Grpc.Core related improvements at https://github.com/grpc/grpc

[wazzamatazz]

The new HttpClient-based client is great, but it’s only an option if you’re using .NET Core 3.0 on the client side. Improving certificate handling for the Grpc.Core-based client as described above would be a great help when working with a target framework that doesn’t support .NET Standard 2.1.