Review TLS support for OC receiver and add tests

[pjanotti]

TLS config for OC receiver is being added via #167 however in light of census-instrumentation/opencensus-service#596 I think we need to revisit the implementation and tests here.

[ccaraman]

@pjanotti I would like to take this one since I'm working on improving oc receiver documentation and test coverage!

[pjanotti]

The code used here should be shared with fix for #126 - in principle it should be possible to share gRPC configuration settings/code between different gRPC receivers and exporters.

[annanay25]

@pjanotti +1

This chunk of code for generating grpc calloptions from the common grpcsettings can also be moved to common, so all exporters/receivers can share? -

opentelemetry-collector/exporter/opencensusexporter/factory.go

Lines 73 to 81 in 63362d5

	if ocac.Endpoint == "" {
	return nil, &ocExporterError{
	code: errEndpointRequired,
	msg: "OpenCensus exporter config requires an Endpoint",
	}
	}
	opts := []ocagent.ExporterOption{ocagent.WithAddress(ocac.Endpoint)}
	if ocac.Compression != "" {
	if compressionKey := compressiongrpc.GetGRPCCompressionKey(ocac.Compression); compressionKey != compression.Unsupported {

[bogdandrutu]

I think we now have ConfigGrpc that has all of these things.

[tonglil]

Hello, can I ask if anyone has tested or gotten an OpenCensus instrumented application using the ocagent exporter to send to a OpenTelemetry collector configured with the OpenCensus receiver, using mTLS (mutual TLS)?

My poc works when the ocagent is set to insecure, as the collector logs the traces.

However when TLS credentials are set on both sides, the ocagent seems to hang on connecting and the collector shows 0 traces.

The same TLS files are valid because they worked with an OT instrumented app and the collector configured with the OT receiver using mTLS.

I feel like I'm missing a piece here and hope to find someone who's been able to confirm or deny if there's a problem with ocagent or the collector? Happy to share my code to reproduce.