feat: exclude OTEL instrumentation via build tag (#770)

* feat: exclude OTEL instrumentation via build tag

* add readme

README.md

@@ -73,6 +73,15 @@ CLIENT_ID=web CLIENT_SECRET=secret ISSUER=http://oidc.local:9998/ SCOPES="openid
 
 > Note: Usernames are suffixed with the hostname (`test-user@localhost` or `test-user@oidc.local`)
 
+
+### Build Tags
+
+The library uses build tags to enable or disable features. The following build tags are available:
+
+| Build Tag | Description                                                                                                                                                              |
+|-----------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `no_otel`  | Disables the OTel instrumentation, which is enabled by default. This is useful if you do not want to use OTel or if you want to use a different instrumentation library. |
+
 ### Server configuration
 
 Example server allows extra configuration using environment variables and could be used for end to

internal/otel/otel.go

@@ -0,0 +1,12 @@
+//go:build !no_otel
+
+package otel
+
+import (
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/trace"
+)
+
+func Tracer(name string) trace.Tracer {
+	return otel.Tracer(name)
+}

internal/otel/shim.go

@@ -0,0 +1,22 @@
+//go:build no_otel
+
+package otel
+
+import (
+	"context"
+)
+
+type FakeTracer struct{}
+type FakeSpan struct{}
+
+func Tracer(name string) FakeTracer {
+	return FakeTracer{}
+}
+
+func (t FakeTracer) Start(ctx context.Context, _ string) (context.Context, FakeSpan) {
+	return ctx, FakeSpan{}
+}
+
+func (s FakeSpan) End() {
+
+}

pkg/client/client.go

@@ -12,7 +12,7 @@ import (
 
 	"github.com/go-jose/go-jose/v4"
 	"github.com/zitadel/logging"
-	"go.opentelemetry.io/otel"
+	"github.com/zitadel/oidc/v3/internal/otel"
 	"golang.org/x/oauth2"
 
 	"github.com/zitadel/oidc/v3/pkg/crypto"

pkg/op/op.go

@@ -8,10 +8,10 @@ import (
 	"time"
 
 	"github.com/go-chi/chi/v5"
-	jose "github.com/go-jose/go-jose/v4"
+	"github.com/go-jose/go-jose/v4"
 	"github.com/rs/cors"
+	"github.com/zitadel/oidc/v3/internal/otel"
 	"github.com/zitadel/schema"
-	"go.opentelemetry.io/otel"
 	"golang.org/x/text/language"
 
 	httphelper "github.com/zitadel/oidc/v3/pkg/http"