[#11] services: Implement universal Sign/Verify service

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/services/util/sign.go

@@ -0,0 +1,44 @@
+package util
+
+import (
+	"context"
+	"crypto/ecdsa"
+
+	"github.com/nspcc-dev/neofs-api-go/v2/signature"
+	"github.com/pkg/errors"
+)
+
+type UnaryHandler func(context.Context, interface{}) (interface{}, error)
+
+type UnarySignService struct {
+	key *ecdsa.PrivateKey
+
+	unaryHandler UnaryHandler
+}
+
+func NewUnarySignService(key *ecdsa.PrivateKey, handler UnaryHandler) *UnarySignService {
+	return &UnarySignService{
+		key:          key,
+		unaryHandler: handler,
+	}
+}
+
+func (s *UnarySignService) HandleUnaryRequest(ctx context.Context, req interface{}) (interface{}, error) {
+	// verify request signatures
+	if err := signature.VerifyServiceMessage(req); err != nil {
+		return nil, errors.Wrap(err, "could not verify request")
+	}
+
+	// process request
+	resp, err := s.unaryHandler(ctx, req)
+	if err != nil {
+		return nil, errors.Wrap(err, "could not handle request")
+	}
+
+	// sign the response
+	if err := signature.SignServiceMessage(s.key, resp); err != nil {
+		return nil, errors.Wrap(err, "could not sign response")
+	}
+
+	return resp, nil
+}