Adds plugin support and a simple plugin as example.

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/stretchr/testify v1.8.4
 	golang.org/x/sys v0.8.0
 	google.golang.org/grpc v1.55.0
+	google.golang.org/protobuf v1.30.0
 )
 
 require (
@@ -24,6 +25,5 @@ require (
 	golang.org/x/text v0.8.0 // indirect
 	golang.org/x/tools v0.6.0 // indirect
 	google.golang.org/genproto v0.0.0-20230306155012-7f2fa6fef1f4 // indirect
-	google.golang.org/protobuf v1.30.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

pkg/plugin/simple-example/simple-example.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net"
+
+	pb "github.com/spiffe/spiffe-helper/pkg/plugin"
+	"google.golang.org/grpc"
+)
+
+type simpleExampleServer struct {
+	pb.SpiffeHelperServer
+}
+
+func (s *simpleExampleServer) PostConfigs(ctx context.Context, request *pb.ConfigsRequest) (*pb.Empty, error) {
+	configs := request.Configs
+
+	fmt.Printf("From: %s\n", configs["from"])
+	fmt.Printf("To: %s\n", configs["to"])
+	fmt.Printf("Message: %s\n", configs["message"])
+
+	return new(pb.Empty), nil
+}
+
+func main() {
+	lis, err := net.Listen("tcp", "localhost:8081")
+	if err != nil {
+		log.Fatalf("failed to listen: %v", err)
+	}
+
+	grpcServer := grpc.NewServer()
+	simpleExampleServer := &simpleExampleServer{}
+	pb.RegisterSpiffeHelperServer(grpcServer, simpleExampleServer)
+	log.Printf("server listening at %v", lis.Addr())
+
+	if err := grpcServer.Serve(lis); err != nil {
+		log.Fatalf("failed to serve: %v", err)
+	}
+}