Add libgit2 checkout test with ED25519 key

This adds a test to detect any regression in libgit2's ED25519 key
support. go-git supports ED25519 but not the current version of
libgit2 used in flux. The updates to libgit2 in v1.2.0 adds support
for ED25519. This test would help ensure the right version of libgit2
is used.

Signed-off-by: Sunny <darkowlzz@protonmail.com>

Author: darkowlzz

pkg/git/libgit2/checkout_test.go

@@ -24,8 +24,12 @@ import (
 	"os"
 	"path"
 	"testing"
+	"time"
 
+	"github.com/fluxcd/pkg/ssh"
 	git2go "github.com/libgit2/git2go/v31"
+	. "github.com/onsi/gomega"
+	corev1 "k8s.io/api/core/v1"
 
 	"github.com/fluxcd/source-controller/pkg/git"
 )
@@ -77,3 +81,48 @@ func TestCheckoutTagSemVer_Checkout(t *testing.T) {
 		t.Errorf("expected semver hash %s, got %s", cTag.Hash(), cSemVer.Hash())
 	}
 }
+
+// This test is specifically to detect regression in libgit2's ED25519 key
+// support.
+// Refer: https://github.com/fluxcd/source-controller/issues/399
+func TestCheckout_ED25519(t *testing.T) {
+	g := NewWithT(t)
+
+	timeout := 5 * time.Second
+	url := "ssh://git@github.com/projectcontour/contour"
+
+	// Fetch github host key.
+	githubHostKey, err := ssh.ScanHostKey("github.com:22", timeout)
+	g.Expect(err).NotTo(HaveOccurred())
+
+	kp, err := ssh.NewEd25519Generator().Generate()
+	g.Expect(err).ToNot(HaveOccurred())
+
+	secret := corev1.Secret{
+		Data: map[string][]byte{
+			"identity":    kp.PrivateKey,
+			"known_hosts": []byte(githubHostKey),
+		},
+	}
+
+	authStrategy, err := AuthSecretStrategyForURL(url)
+	g.Expect(err).ToNot(HaveOccurred())
+	gitAuth, err := authStrategy.Method(secret)
+	g.Expect(err).ToNot(HaveOccurred())
+
+	branchCheckoutStrat := &CheckoutBranch{branch: "main"}
+	tmpDir, _ := os.MkdirTemp("", "test")
+	defer os.RemoveAll(tmpDir)
+
+	ctx, cancel := context.WithTimeout(context.TODO(), timeout)
+	defer cancel()
+
+	// This should always fail because the generated key above isn't present in
+	// the git server.
+	_, _, err = branchCheckoutStrat.Checkout(ctx, tmpDir, url, gitAuth)
+	g.Expect(err).To(HaveOccurred())
+
+	// NOTE: Flip this condition once libgit2 build update in
+	// https://github.com/fluxcd/source-controller/pull/437 gets merged.
+	g.Expect(err.Error()).To(ContainSubstring("Unable to extract public key from private key"))
+}