Make OtlpExporterOptions.HttpClientFactory work with GRPC protocol

[dhhoang]

Fixes #2120, #2009
Design discussion issue #3393

Changes

The purpose is to make it possible to control how HttpClient is created when using GRPC protocol. A common use case is to submit a client certificate, for example, to use with mTLS. The changes include:

• Makes OtlpExporterOptions.HttpClientFactory option work with OtlpExportProtocol.Grpc protocol, instead of just OtlpExportProtocol.HttpProtobuf.
• The HttpClient instance is created once when the channel is created, and it is passed to GrpcChannelOptions.
• In addition, the use of IHttpClientFactory is also supported for GRPC in much the same way it is for HttpProtobuf.

Usage

The following code shows how to setup client certificate with this option enabled.

Services.AddOpenTelemetry().WithTracing(b =>
{
  b.AddOtlpExporter(expoterOpts=>{
    expoterOpts.Protocol = OtlpExportProtocol.Grpc;
    expoterOpts.HttpClientFactory = CreateOTLPHttpClient;
  });
});

private static HttpClient CreateOTLPHttpClient()
{
  var handler = new HttpClientHandler
  {
    ClientCertificateOptions = ClientCertificateOption.Manual,
    // use this to disable peer validation
    ServerCertificateCustomValidationCallback =HttpClientHandler.DangerousAcceptAnyServerCertificateValidator
  };
  handler.ClientCertificates.Add(new X509Certificate2("mycert.pfx"));

  return new HttpClient(handler, true);
}

Merge requirement checklist

• CONTRIBUTING guidelines followed (nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable) (N/A)

[codecov]

Codecov Report

Merging #4625 (3c421d2) into main (104cf32) will increase coverage by 0.02%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4625      +/-   ##
==========================================
+ Coverage   84.90%   84.93%   +0.02%     
==========================================
  Files         313      313              
  Lines       12609    12616       +7     
==========================================
+ Hits        10706    10715       +9     
+ Misses       1903     1901       -2     

Impacted Files	Coverage Δ
...orter.OpenTelemetryProtocol/OtlpExporterOptions.cs	96.36% <ø> (ø)
...TelemetryProtocol/OtlpExporterOptionsExtensions.cs	97.02% <100.00%> (+0.22%)	⬆️

... and 2 files with indirect coverage changes

[vishweshbankwar]

Thanks @dhhoang The proposed change looks reasonable to me, was going to send the same PR shortly 😆

Adding @alanwest @CodeBlanch @utpilla to share feedback on proposal before reviewing.

[alanwest]

@dhhoang Supporting the HttpClientFactory option with the gRPC exporter is something we're considering.

Though, if your need is primarily with the lack of support for client certificates, I think I'd be interested if we first pursued the configuration options currently missing that are required by the spec: Certificate file, Client key file, and Client certificate file.

[dhhoang]

@dhhoang Supporting the HttpClientFactory option with the gRPC exporter is something we're considering.

Though, if your need is primarily with the lack of support for client certificates, I think I'd be interested if we first pursued the configuration options currently missing that are required by the spec: Certificate file, Client key file, and Client certificate file.

@alanwest I'm actually about to send another PR to enable these configs, since they're needed for mTLS to work with .NET Framework targets.
That being said the ability to control HttpClient would be useful for other use cases (proxies etc.).
I saw the issue mentioned in #4616 and have made a comment there.

[alanwest]

I'm actually about to send another PR to enable these configs, since they're needed for mTLS to work with .NET Framework targets.

Sounds good! For now, I think we could definitely proceed with the addition of the missing config options.

[github-actions]

This PR was marked stale due to lack of activity and will be closed in 7 days. Commenting or Pushing will instruct the bot to automatically remove the label. This bot runs once per day.

[github-actions]

Closed as inactive. Feel free to reopen if this PR is still being worked on.