fix(auth): restore OpenTelemetry handling in transports

* Based on googleapis/google-api-go-client#2127

fixes: #10962

auth/go.mod

@@ -8,13 +8,21 @@ require (
 	github.com/google/s2a-go v0.1.8
 	github.com/googleapis/enterprise-certificate-proxy v0.3.4
 	go.opencensus.io v0.24.0
+	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.49.0
+	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.54.0
 	golang.org/x/net v0.29.0
 	google.golang.org/grpc v1.66.2
 	google.golang.org/protobuf v1.34.2
 )
 
 require (
+	github.com/felixge/httpsnoop v1.0.4 // indirect
+	github.com/go-logr/logr v1.4.2 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
+	go.opentelemetry.io/otel v1.29.0 // indirect
+	go.opentelemetry.io/otel/metric v1.29.0 // indirect
+	go.opentelemetry.io/otel/trace v1.29.0 // indirect
 	golang.org/x/crypto v0.27.0 // indirect
 	golang.org/x/oauth2 v0.22.0 // indirect
 	golang.org/x/sync v0.8.0 // indirect

auth/go.sum

@@ -6,11 +6,19 @@ github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/cncf/udpa/go v0.0.0-20191209042840-269d4d468f6f/go.mod h1:M8M6+tZqaGXZJjfX53e64911xZQV5JYwmTeXPW+k8Sc=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/envoyproxy/go-control-plane v0.9.0/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
 github.com/envoyproxy/go-control-plane v0.9.1-0.20191026205805-5f8ba28d4473/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
 github.com/envoyproxy/go-control-plane v0.9.4/go.mod h1:6rpuAdCZL397s3pYoYcLgu1mIlRU8Am5FuJP05cCM98=
 github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
+github.com/felixge/httpsnoop v1.0.4 h1:NFTV2Zj1bL4mc9sqWACXbQFVBBg2W3GPvqp8/ESS2Wg=
+github.com/felixge/httpsnoop v1.0.4/go.mod h1:m8KPJKqk1gH5J9DgRY2ASl2lWCfGKXixSwevea8zH2U=
+github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
+github.com/go-logr/logr v1.4.2 h1:6pFjapn8bFcIbiKo3XT4j/BhANplGihG6tvd+8rYgrY=
+github.com/go-logr/logr v1.4.2/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
+github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
+github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
 github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
 github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da h1:oI5xCqsCo564l8iNU+DwB5epxmsaqB+rhGL0m5jtYqE=
@@ -40,6 +48,7 @@ github.com/google/s2a-go v0.1.8/go.mod h1:6iNWHTpQ+nfNRN5E00MSdfDwVesa8hhS32PhPO
 github.com/google/uuid v1.1.2/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/googleapis/enterprise-certificate-proxy v0.3.4 h1:XYIDZApgAnrN1c855gTgghdIA6Stxb52D5RnLI1SLyw=
 github.com/googleapis/enterprise-certificate-proxy v0.3.4/go.mod h1:YKe7cfqYXjKGpGvmSg28/fFvhNzinZQm8DGnaburhGA=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/prometheus/client_model v0.0.0-20190812154241-14fe0d1b01d4/go.mod h1:xMI15A0UPsDsEKsMN9yxemIoYk6Tm2C1GtYGdfGttqA=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
@@ -48,8 +57,20 @@ github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpE
 github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
 github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
+github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
+github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
 go.opencensus.io v0.24.0 h1:y73uSU6J157QMP2kn2r30vwW1A2W2WFwSCGnAVxeaD0=
 go.opencensus.io v0.24.0/go.mod h1:vNK8G9p7aAivkbmorf4v+7Hgx+Zs0yY+0fOtgBfjQKo=
+go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.49.0 h1:4Pp6oUg3+e/6M4C0A/3kJ2VYa++dsWVTtGgLVj5xtHg=
+go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.49.0/go.mod h1:Mjt1i1INqiaoZOMGR1RIUJN+i3ChKoFRqzrRQhlkbs0=
+go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.54.0 h1:TT4fX+nBOA/+LUkobKGW1ydGcn+G3vRw9+g5HwCphpk=
+go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.54.0/go.mod h1:L7UH0GbB0p47T4Rri3uHjbpCFYrVrwc1I25QhNPiGK8=
+go.opentelemetry.io/otel v1.29.0 h1:PdomN/Al4q/lN6iBJEN3AwPvUiHPMlt93c8bqTG5Llw=
+go.opentelemetry.io/otel v1.29.0/go.mod h1:N/WtXPs1CNCUEx+Agz5uouwCba+i+bJGFicT8SR4NP8=
+go.opentelemetry.io/otel/metric v1.29.0 h1:vPf/HFWTNkPu1aYeIsc98l4ktOQaL6LeSoeV2g+8YLc=
+go.opentelemetry.io/otel/metric v1.29.0/go.mod h1:auu/QWieFVWx+DmQOUMgj0F8LHWdgalxXqvp7BII/W8=
+go.opentelemetry.io/otel/trace v1.29.0 h1:J/8ZNK4XgR7a21DZUAsbF8pZ5Jcw1VhACmnYt39JTi4=
+go.opentelemetry.io/otel/trace v1.29.0/go.mod h1:eHl3w0sp3paPkYstJOmAimxhiFXPg+MMTlEh3nsQgWQ=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/crypto v0.27.0 h1:GXm2NjJrPaiv/h1tb2UH8QfgC/hOf/+z0p6PT8o1w7A=
@@ -117,6 +138,7 @@ google.golang.org/protobuf v1.34.2 h1:6xV6lTsCfpGD21XK49h7MhtcApnLqkfYgPcdHftf6h
 google.golang.org/protobuf v1.34.2/go.mod h1:qYOHts0dSfpeUzUFpOMr/WGzszTmLH+DiWniOlNbLDw=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
 honnef.co/go/tools v0.0.0-20190523083050-ea95bdfd59fc/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=

auth/grpctransport/grpctransport.go

@@ -23,15 +23,18 @@ import (
 	"fmt"
 	"net/http"
 	"os"
+	"sync"
 
 	"cloud.google.com/go/auth"
 	"cloud.google.com/go/auth/credentials"
 	"cloud.google.com/go/auth/internal"
 	"cloud.google.com/go/auth/internal/transport"
 	"go.opencensus.io/plugin/ocgrpc"
+	"go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc"
 	"google.golang.org/grpc"
 	grpccreds "google.golang.org/grpc/credentials"
 	grpcinsecure "google.golang.org/grpc/credentials/insecure"
+	"google.golang.org/grpc/stats"
 )
 
 const (
@@ -49,6 +52,27 @@ var (
 	timeoutDialerOption grpc.DialOption
 )
 
+// otelStatsHandler is a singleton otelgrpc.clientHandler to be used across
+// all dial connections to avoid the memory leak documented in
+// https://github.com/open-telemetry/opentelemetry-go-contrib/issues/4226
+//
+// TODO: When this module depends on a version of otelgrpc containing the fix,
+// replace this singleton with inline usage for simplicity.
+// The fix should be in https://github.com/open-telemetry/opentelemetry-go/pull/5797.
+var (
+	initOtelStatsHandlerOnce sync.Once
+	otelStatsHandler         stats.Handler
+)
+
+// otelGRPCStatsHandler returns singleton otelStatsHandler for reuse across all
+// dial connections.
+func otelGRPCStatsHandler() stats.Handler {
+	initOtelStatsHandlerOnce.Do(func() {
+		otelStatsHandler = otelgrpc.NewClientHandler()
+	})
+	return otelStatsHandler
+}
+
 // ClientCertProvider is a function that returns a TLS client certificate to be
 // used when opening TLS connections. It follows the same semantics as
 // [crypto/tls.Config.GetClientCertificate].
@@ -295,6 +319,7 @@ func dial(ctx context.Context, secure bool, opts *Options) (*grpc.ClientConn, er
 	// gRPC stats handler.
 	// This assumes that gRPC options are processed in order, left to right.
 	grpcOpts = addOCStatsHandler(grpcOpts, opts)
+	grpcOpts = addOpenTelemetryStatsHandler(grpcOpts, opts)
 	grpcOpts = append(grpcOpts, opts.GRPCDialOpts...)
 
 	return grpc.NewClient(endpoint, grpcOpts...)
@@ -398,3 +423,10 @@ func addOCStatsHandler(dialOpts []grpc.DialOption, opts *Options) []grpc.DialOpt
 	}
 	return append(dialOpts, grpc.WithStatsHandler(&ocgrpc.ClientHandler{}))
 }
+
+func addOpenTelemetryStatsHandler(dialOpts []grpc.DialOption, opts *Options) []grpc.DialOption {
+	if opts.DisableTelemetry {
+		return dialOpts
+	}
+	return append(dialOpts, grpc.WithStatsHandler(otelGRPCStatsHandler()))
+}

auth/httptransport/transport.go

@@ -28,6 +28,7 @@ import (
 	"cloud.google.com/go/auth/internal/transport"
 	"cloud.google.com/go/auth/internal/transport/cert"
 	"go.opencensus.io/plugin/ochttp"
+	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
 	"golang.org/x/net/http2"
 )
 
@@ -42,6 +43,9 @@ func newTransport(base http.RoundTripper, opts *Options) (http.RoundTripper, err
 		headers: headers,
 	}
 	var trans http.RoundTripper = ht
+	// Give OpenTelemetry precedence over OpenCensus in case user configuration
+	// causes both to write the same header (`X-Cloud-Trace-Context`).
+	trans = addOpenTelemetryTransport(trans, opts)
 	trans = addOCTransport(trans, opts)
 	switch {
 	case opts.DisableAuthentication:
@@ -163,6 +167,13 @@ func (t *headerTransport) RoundTrip(req *http.Request) (*http.Response, error) {
 	return rt.RoundTrip(&newReq)
 }
 
+func addOpenTelemetryTransport(trans http.RoundTripper, opts *Options) http.RoundTripper {
+	if opts.DisableTelemetry {
+		return trans
+	}
+	return otelhttp.NewTransport(trans)
+}
+
 func addOCTransport(trans http.RoundTripper, opts *Options) http.RoundTripper {
 	if opts.DisableTelemetry {
 		return trans