Setup secure sandboxed development environment on macOS with Podman and Secretive

!README.md

Why

See article: Devcontainers, Little Snitch, macOS TCC - protecting developer laptops

How To

1. Install Secretive using brew install --cask secretive, then launch Secretive App.

2. Create a new secret that requires authentication, named gitsign. You will need to perform biometric authentication each time this key is used.

3. Create a new secret that notify only, named github. This key is used for performing git pull/push/fetch from GitHub.

4. Add gitsign public key to SSH "Signing keys" on Github Settings Page. Title is not required.

5. Add github public key to SSH "Authentication keys" on Github Settings Page. Title is not required.

   

6. Edit .zshenv.

   cat >> ~/.zshenv <<EOF
   # For git commit signing
   export SSH_AUTH_SOCK="$HOME/Library/Containers/com.maxgoedjen.Secretive.SecretAgent/Data/socket.ssh"
   
   EOF
   
   # For some GPU-acceleration within podman
   # Setup: https://podman-desktop.io/docs/installation/macos-install#using-libkrun-as-machine-provider
   # Usage: https://podman-desktop.io/docs/podman/gpu
   cat >> ~/.zshenv <<'EOF'
   # Enable some GPU-acceleration within podman
   if [[ "$(uname -m)" == "arm64" ]]; then
     export CONTAINERS_MACHINE_PROVIDER=libkrun
   fi
   
   EOF
   
   # Activate in current shell session
   source ~/.zshenv

7. (Recommended) Install podman to protect against exploits that triggers immediately upon opening a git repository or workspace. See: Why are dev containers important?

   # Install podman CLI using official pkg installer (from GitHub)
   # See: https://podman.io/docs/installation#macos
   open https://github.com/containers/podman/releases
   # Manually download and run `podman-installer-macos-arm64.pkg` from latest release
   
   # Create a virtual machine with no access to the host folders
   # See: https://docs.podman.io/en/latest/markdown/podman-machine-init.1.html#volume-v-source-target-options
   podman machine init -v ''
   
   # Use 8Gib or RAM for the VM
   podman machine set --memory 8192

8. Edit .ssh/config. You may omit the first section that enables VSCode or your IDE to perform Sandboxed Development via podman (including the ability to gitsign without revealing SSH private keys), though it’s strongly recommended.

   cat >> ~/.ssh/config <<EOF
   # For git commit signing within podman
   Host podman-machine-default
     HostName localhost
     # From: podman machine inspect | jq '.[0].SSHConfig'
     IdentityFile $(podman machine inspect | jq -r '.[0].SSHConfig.IdentityPath')
     Port $(podman machine inspect | jq -r '.[0].SSHConfig.Port')
     User $(podman machine inspect | jq -r '.[0].SSHConfig.RemoteUsername')
     IdentitiesOnly yes
     StrictHostKeyChecking no
     UserKnownHostsFile /dev/null
     CheckHostIP no
     LogLevel ERROR
     SetEnv LC_ALL=
     ForwardAgent yes
   
   # For git authentication
   Host *
     IdentityAgent $HOME/Library/Containers/com.maxgoedjen.Secretive.SecretAgent/Data/socket.ssh
   EOF

9. Install a newer version of git that supports signingkey = key::xxxx format. As of this writing, the latest macOS (Sequoia 15.5) comes with a pre-installed version of Git that is outdated.

   #/bin/bash -c "$(curl --proto '=https' --tlsv1.3 -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
   brew install git

10. Update .gitconfig replacing the name and email with your github account. Replace the signingkey with your gitsign public key. Do remember to add back the key:: prefix.

    # Set user info
    git config --global user.name "heri16"
    git config --global user.email "[email protected]"
    
    # Ser user signingkey
    git config --global user.signingkey "key::ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBMYmjVIE8ERSgs7EEHbYwhCgMx1v0ijKmmCt1ku0yBvjDIoddBi6P9QSALVXnTGp+PinT5l4JFWGV77QxfiypDw= [email protected]"
    git config --global gpg.format ssh
    
    # Push and signing settings
    git config --global commit.gpgSign true
    git config --global tag.gpgSign true
    git config --global tag.forceSignAnnotated true
    git config --global push.default current
    git config --global push.gpgSign if-asked
    
    # Enable git commit verification
    mkdir -p ~/.config/git
    echo "heri16 ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBMYmjVIE8ERSgs7EEHbYwhCgMx1v0ijKmmCt1ku0yBvjDIoddBi6P9QSALVXnTGp+PinT5l4JFWGV77QxfiypDw= [email protected]" >> ~/.config/git/allowed_signers
    git config --global gpg.ssh.allowedSignersFile ~/.config/git/allowed_signers

11. Confirm that Secretive Agent is running: ssh-add -l. If not, restart your Terminal.

12. Do a test commit. You should see Good "git" signature for heri16 with ECDSA key SHA256:ZSJWE2tfNICQ92hpNZnfW7vihJB/ToZz5E1mil3GE10

    touch test.md && git add test.md && git commit -S -m "test commit"
    git log --show-signature
    git reset --soft HEAD~1 

13. Ensure that your future commits on GitHub show a Green Verified badge

14. Retroactively sign your past commits:

    git rebase -i --exec 'author=$(git show -s --format="%ae"); me=$(git config user.email); [ "$author" = "$me" ] && git commit --amend --no-edit -S || echo "Skip $author"' HEAD~N

    Replace N with how many commits back you want to rebase (e.g., HEAD~10 for last 10 commits).

15. Apply security hardening to podman virtual machine:

    • Additional sandboxing to protect against container breakout and escapes: https://gist.github.com/heri16/60acf5b57518cd8518e62f1ce74f14a8

16. Learn how to open a git repository within a Dev Container using your preferred IDE:

    • Guide for VScode
      1. Start the VM in Terminal: podman machine start
      2. Install Official Remote Development Extensions for VScode
      3. Set Setting -> GitHub: Git Protocol to: ssh
      4. Remote-SSH: Connect to Host -> podman-machine-default
      5. Dev Containers: Clone Repository in Container Volume -> Select repo with .devcontainer
    • Guide for IntelliJ

.gitconfig

[user]
	name = heri16
	email = [email protected]
	signingkey = key::ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBMYmjVIE8ERSgs7EEHbYwhCgMx1v0ijKmmCt1ku0yBvjDIoddBi6P9QSALVXnTGp+PinT5l4JFWGV77QxfiypDw= [email protected]
[push]
	default = current
	gpgSign = if-asked
[commit]
	gpgSign = true
[gpg]
	format = ssh
[tag]
	gpgSign = true
	forceSignAnnotated = true
[gpg "ssh"]
	allowedSignersFile = /Users/user0/.config/git/allowed_signers

.ssh_config

# For git commit signing within podman
Host podman-machine-default
	HostName localhost
	# From: podman machine inspect | jq '.[0].SSHConfig'
	IdentityFile /Users/user0/.local/share/containers/podman/machine/machine
	Port 60877
	User core
	IdentitiesOnly yes
	StrictHostKeyChecking no
	UserKnownHostsFile /dev/null
	CheckHostIP no
	LogLevel ERROR
	SetEnv LC_ALL=
	ForwardAgent yes

# For git authentication
Host *
	IdentityAgent /Users/user0/Library/Containers/com.maxgoedjen.Secretive.SecretAgent/Data/socket.ssh

.zshenv

# For git commit signing
export SSH_AUTH_SOCK=/Users/user0/Library/Containers/com.maxgoedjen.Secretive.SecretAgent/Data/socket.ssh

# For some GPU-acceleration within podman
export CONTAINERS_MACHINE_PROVIDER=libkrun

Inspired by:

• Devcontainers, Little Snitch, macOS TCC - protecting developer laptops