feat: enable grpc server reflection (#5689)

This change enables [gRPC server
reflection](https://github.com/grpc/grpc-go/blob/master/Documentation/server-reflection-tutorial.md).
It allows for easier setting up of dev-tools like
[gRPCurl](https://github.com/fullstorydev/grpcurl) and
[gRPCui](https://github.com/fullstorydev/grpcui).

To see it in action, after you start zitadel on the localhost:

```
go install github.com/fullstorydev/grpcui/cmd/grpcui@latest
grpcui -plaintext localhost:8080
````


![image](https://user-images.githubusercontent.com/5411563/232060184-1a114640-e87a-48da-866f-ff8d597e790f.png)

internal/api/api.go

@@ -12,6 +12,7 @@ import (
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/health"
 	healthpb "google.golang.org/grpc/health/grpc_health_v1"
+	"google.golang.org/grpc/reflection"
 
 	internal_authz "github.com/zitadel/zitadel/internal/api/authz"
 	"github.com/zitadel/zitadel/internal/api/grpc/server"
@@ -71,6 +72,7 @@ func New(
 	api.RegisterHandlerOnPrefix("/debug", api.healthHandler())
 	api.router.Handle("/", http.RedirectHandler(login.HandlerPrefix, http.StatusFound))
 
+	reflection.Register(api.grpcServer)
 	return api, nil
 }
 

internal/api/grpc/probes.go

@@ -1,5 +1,12 @@
 package grpc
 
+import (
+	"path"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/reflection/grpc_reflection_v1alpha"
+)
+
 const (
 	Healthz    = "/Healthz"
 	Readiness  = "/Ready"
@@ -9,3 +16,18 @@ const (
 var (
 	Probes = []string{Healthz, Readiness, Validation}
 )
+
+func init() {
+	Probes = append(Probes, AllPaths(grpc_reflection_v1alpha.ServerReflection_ServiceDesc)...)
+}
+
+func AllPaths(sd grpc.ServiceDesc) []string {
+	paths := make([]string, 0, len(sd.Methods)+len(sd.Streams))
+	for _, method := range sd.Methods {
+		paths = append(paths, path.Join("/", sd.ServiceName, method.MethodName))
+	}
+	for _, stream := range sd.Streams {
+		paths = append(paths, path.Join("/", sd.ServiceName, stream.StreamName))
+	}
+	return paths
+}

internal/api/grpc/probes_test.go

@@ -0,0 +1,32 @@
+package grpc
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/reflection/grpc_reflection_v1alpha"
+)
+
+func TestAllPaths(t *testing.T) {
+	type args struct {
+		sd grpc.ServiceDesc
+	}
+	tests := []struct {
+		name string
+		args args
+		want []string
+	}{
+		{
+			name: "server reflection",
+			args: args{grpc_reflection_v1alpha.ServerReflection_ServiceDesc},
+			want: []string{"/grpc.reflection.v1alpha.ServerReflection/ServerReflectionInfo"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := AllPaths(tt.args.sd)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}