$ echo 'world' >> hello.md &&\
GIT_AUTHOR_DATE="2025-01-30T10:00:00" \
GIT_COMMITTER_DATE="2025-01-30T10:00:00" \
GIT_TRACE=1 \
git commit -S -m "Add world to hello.md" -a
15:05:21.287907 exec-cmd.c:139          trace: resolved executable path from Darwin stack: /Library/Developer/CommandLineTools/usr/bin/git
15:05:21.288536 exec-cmd.c:238          trace: resolved executable dir: /Library/Developer/CommandLineTools/usr/bin
15:05:21.289179 git.c:460               trace: built-in: git commit -S -m 'Add world to hello.md' -a
15:05:21.291569 run-command.c:655       trace: run_command: ssh-keygen -Y sign -n git -f /Users/george/.ssh/id_ed25519.pub /var/folders/9b/92pmw3kx35gc39k132myqnrh0000gp/T//.git_signing_buffer_tmp5jyYqa
15:05:21.299105 run-command.c:655       trace: run_command: git maintenance run --auto --no-quiet
15:05:21.302676 exec-cmd.c:139          trace: resolved executable path from Darwin stack: /Library/Developer/CommandLineTools/usr/libexec/git-core/git
15:05:21.303064 exec-cmd.c:238          trace: resolved executable dir: /Library/Developer/CommandLineTools/usr/libexec/git-core
15:05:21.303562 git.c:460               trace: built-in: git maintenance run --auto --no-quiet
[main f0e8459] Add world to hello.md
 1 file changed, 1 insertion(+)

package main

import (
	"log"
	"os"
	"path/filepath"
	"time"

	"github.com/go-git/go-git/v5"
	"github.com/go-git/go-git/v5/plumbing/object"
	"github.com/go-git/go-git/v5/plumbing/sign"
)

func main() {
	repo, err := git.PlainOpen("/tmp/repo")
	if err != nil {
		panic(err)
	}

	filePath := filepath.Join("/tmp/repo", "hello.md")
	f, err := os.OpenFile(filePath, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0644)
	if err != nil {
		panic(err)
	}
	if _, err := f.WriteString("world\n"); err != nil {
		panic(err)
	}
	f.Close()

	w, err := repo.Worktree()
	if err != nil {
		panic(err)
	}

	_, err = w.Add("hello.md")
	if err != nil {
		panic(err)
	}

	// Just add signing options directly to CommitOptions
	signer, err := sign.NewSSHSigner("~/.ssh/id_ed25519")
	if err != nil {
		panic(err)
	}
	if signer == nil {
		println(signer)
	}

	pacific, err := time.LoadLocation("America/Los_Angeles")
	if err != nil {
		log.Fatalf("Failed to load location: %v", err)
	}

	commitTime := time.Date(2025, 1, 30, 10, 0, 0, 0, pacific) // Fixed timestamp to compare hashes

	commit, err := w.Commit("Add world to hello.md\n", &git.CommitOptions{
		Author: &object.Signature{
			Name:  "Roshan George",
			Email: "roshan@technologybrother.com",
			When:  commitTime,
		},
		Committer: &object.Signature{
			Name:  "Roshan George",
			Email: "roshan@technologybrother.com",
			When:  commitTime,
		},
		Signer: signer,
	})

	if err != nil {
		panic(err)
	}

	println("Created commit:", commit.String())
}

$ go run main.go
Created commit: f0e845969b5111d5702c789b311d645db6d32f95

git cat-file commit f0e845969b5111d5702c789b311d645db6d32f95
tree ca2a84cb39938f998132a519c5a51ea58f61e957
parent 9ea36ed0ea144e777ba6bd3022d70bf02684ae6b
author Roshan George <roshan@technologybrother.com> 1738260000 -0800
committer Roshan George <roshan@technologybrother.com> 1738260000 -0800
gpgsig -----BEGIN SSH SIGNATURE-----
 U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgsv4P1Kgi/8X6hZ+gemfiQtGSb9
 Urcu7HeA8dWDwXW9oAAAADZ2l0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5
 AAAAQCivvTPR26w4AM+BukWBCQ9fNQ0UUMwi3scjxV5sbFOT3+eRDzddZX8hiwigdzcTOf
 ZZJFiQ68bQZI3PEIBYOAQ=
 -----END SSH SIGNATURE-----

Add world to hello.md