Pass TLS credentials to gRPC server pseudo-node without modifying the ApplicationConfiguration

[tiziano88]

oak/oak/server/rust/oak_loader/src/main.rs

Lines 88 to 96 in ca7f1ee

	// Assign a TLS identity to all gRPC server nodes in the application configuration.
	let grpc_tls_private_key = read_file(&opt.grpc_tls_private_key)?;
	let grpc_tls_certificate = read_file(&opt.grpc_tls_certificate)?;
	for node in &mut app_config.node_configs {
	if let Some(GrpcServerConfig(ref mut grpc_server_config)) = node.config_type {
	grpc_server_config.grpc_tls_private_key = grpc_tls_private_key.clone();
	grpc_server_config.grpc_tls_certificate = grpc_tls_certificate.clone();
	}
	}

Apart from not being very idiomatic (why does oak_loader modify the ApplicationConfiguration object that was supposed to run?), it is problematic for #917 and other related refactorings.

I guess the final solution may be dependant on #689 , but in the meanwhile we can just pass the TLS credentials directly to the Runtime object, and have that propagate them to the gRPC pseudo-node at creation time.

[tiziano88]

@ipetr0v have you started work on this? If not, I can look into it, since it helps with #917

[ipetr0v]

No, I haven't yet.
Thanks for looking into this!

[tiziano88]

Happy to take a look myself as part of #917, thanks!