From 970c5307bdf728c9fb3d338be99d419139f4ecec Mon Sep 17 00:00:00 2001
From: Yoav Amit <yoav@squareup.com>
Date: Tue, 20 Aug 2024 18:37:02 -0400
Subject: plumbing: signature, support the same x509 signature formats as git

Commits and tags signed with x509 certificates may be encoded with the `SIGNED MESSAGE` PEM label.
This behavior is consistent in [git](https://github.com/git/git/blob/master/gpg-interface.c\#L63) and [gpgsm](https://github.com/gpg/gnupg/blob/master/sm/sign.c\#L650) which is commonly used to produce these types of signatures.
---
 plumbing/object/signature.go      |  1 +
 plumbing/object/signature_test.go | 15 ++++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/plumbing/object/signature.go b/plumbing/object/signature.go
index 91cf371..f9c3d30 100644
--- a/plumbing/object/signature.go
+++ b/plumbing/object/signature.go
@@ -19,6 +19,7 @@ var (
 	// a PKCS#7 (S/MIME) signature.
 	x509SignatureFormat = signatureFormat{
 		[]byte("-----BEGIN CERTIFICATE-----"),
+		[]byte("-----BEGIN SIGNED MESSAGE-----"),
 	}
 
 	// sshSignatureFormat is the format of an SSH signature.
diff --git a/plumbing/object/signature_test.go b/plumbing/object/signature_test.go
index 3b20cde..732aa09 100644
--- a/plumbing/object/signature_test.go
+++ b/plumbing/object/signature_test.go
@@ -33,7 +33,7 @@ MKEQruIQWJb+8HVXwssA4=
 			want: signatureTypeSSH,
 		},
 		{
-			name: "known signature format (X509)",
+			name: "known signature format (X509) CERTIFICATE",
 			b: []byte(`-----BEGIN CERTIFICATE-----
 MIIDZjCCAk6gAwIBAgIJALZ9Z3Z9Z3Z9MA0GCSqGSIb3DQEBCwUAMIGIMQswCQYD
 VQQGEwJTRTEOMAwGA1UECAwFVGV4YXMxDjAMBgNVBAcMBVRleGFzMQ4wDAYDVQQK
@@ -45,6 +45,19 @@ ggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIBAQDQZ9Z3Z9Z3Z9Z3Z9Z3Z9Z3
 -----END CERTIFICATE-----`),
 			want: signatureTypeX509,
 		},
+		{
+			name: "known signature format (x509) SIGNED MESSAGE",
+			b: []byte(`-----BEGIN SIGNED MESSAGE-----
+MIIDZjCCAk6gAwIBAgIJALZ9Z3Z9Z3Z9MA0GCSqGSIb3DQEBCwUAMIGIMQswCQYD
+VQQGEwJTRTEOMAwGA1UECAwFVGV4YXMxDjAMBgNVBAcMBVRleGFzMQ4wDAYDVQQK
+DAVUZXhhczEOMAwGA1UECwwFVGV4YXMxGDAWBgNVBAMMD1RleGFzIENlcnRpZmlj
+YXRlMB4XDTE3MDUyNjE3MjY0MloXDTI3MDUyNDE3MjY0MlowgYgxCzAJBgNVBAYT
+AlNFMQ4wDAYDVQQIDAVUZXhhczEOMAwGA1UEBwwFVGV4YXMxDjAMBgNVBAoMBVRl
+eGFzMQ4wDAYDVQQLDAVUZXhhczEYMBYGA1UEAwwPVGV4YXMgQ2VydGlmaWNhdGUw
+ggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIBAQDQZ9Z3Z9Z3Z9Z3Z9Z3Z9Z3
+-----END SIGNED MESSAGE-----`),
+			want: signatureTypeX509,
+		},
 		{
 			name: "unknown signature format",
 			b: []byte(`-----BEGIN ARBITRARY SIGNATURE-----
-- 
cgit