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feat: add ssh_signing_key input for SSH commit signing (#784)
* feat: add ssh_signing_key input for SSH commit signing Add a new ssh_signing_key input that allows passing an SSH signing key for commit signing, as an alternative to the existing use_commit_signing (which uses GitHub API-based commits). When ssh_signing_key is provided: - Git is configured to use SSH signing (gpg.format=ssh, commit.gpgsign=true) - The key is written to ~/.ssh/claude_signing_key with 0600 permissions - Git CLI commands are used (not MCP file ops) - The key is cleaned up in a post step for security Behavior matrix: | ssh_signing_key | use_commit_signing | Result | |-----------------|-------------------|--------| | not set | false | Regular git, no signing | | not set | true | GitHub API (MCP), verified commits | | set | false | Git CLI with SSH signing | | set | true | Git CLI with SSH signing (ssh_signing_key takes precedence) * docs: add SSH signing key documentation - Update security.md with detailed setup instructions for both signing options - Explain that ssh_signing_key enables full git CLI operations (rebasing, etc.) - Add ssh_signing_key to inputs table in usage.md - Update bot_id/bot_name descriptions to note they're needed for verified commits * fix: address security review feedback for SSH signing - Write SSH key atomically with mode 0o600 (fixes TOCTOU race condition) - Create .ssh directory with mode 0o700 (SSH best practices) - Add input validation for SSH key format - Remove unused chmod import - Add tests for validation logic
This commit is contained in:
Ashwin Bhat
@@ -38,7 +38,64 @@ The following permissions are requested but not yet actively used. These will en
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## Commit Signing
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Commits made by Claude through this action are no longer automatically signed with commit signatures. To enable commit signing set `use_commit_signing: True` in the workflow(s). This ensures the authenticity and integrity of commits, providing a verifiable trail of changes made by the action.
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By default, commits made by Claude are unsigned. You can enable commit signing using one of two methods:
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### Option 1: GitHub API Commit Signing (use_commit_signing)
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This uses GitHub's API to create commits, which automatically signs them as verified from the GitHub App:
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```yaml
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- uses: anthropics/claude-code-action@main
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with:
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use_commit_signing: true
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```
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This is the simplest option and requires no additional setup. However, because it uses the GitHub API instead of git CLI, it cannot perform complex git operations like rebasing, cherry-picking, or interactive history manipulation.
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### Option 2: SSH Signing Key (ssh_signing_key)
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This uses an SSH key to sign commits via git CLI. Use this option when you need both signed commits AND standard git operations (rebasing, cherry-picking, etc.):
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```yaml
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- uses: anthropics/claude-code-action@main
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with:
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ssh_signing_key: ${{ secrets.SSH_SIGNING_KEY }}
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bot_id: "YOUR_GITHUB_USER_ID"
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bot_name: "YOUR_GITHUB_USERNAME"
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```
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Commits will show as verified and attributed to the GitHub account that owns the signing key.
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**Setup steps:**
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1. Generate an SSH key pair for signing:
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```bash
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ssh-keygen -t ed25519 -f ~/.ssh/signing_key -N "" -C "commit signing key"
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```
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2. Add the **public key** to your GitHub account:
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- Go to GitHub → Settings → SSH and GPG keys
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- Click "New SSH key"
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- Select **Key type: Signing Key** (important)
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- Paste the contents of `~/.ssh/signing_key.pub`
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3. Add the **private key** to your repository secrets:
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- Go to your repo → Settings → Secrets and variables → Actions
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- Create a new secret named `SSH_SIGNING_KEY`
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- Paste the contents of `~/.ssh/signing_key`
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4. Get your GitHub user ID:
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```bash
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gh api users/YOUR_USERNAME --jq '.id'
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```
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5. Update your workflow with `bot_id` and `bot_name` matching the account where you added the signing key.
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**Note:** If both `ssh_signing_key` and `use_commit_signing` are provided, `ssh_signing_key` takes precedence.
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## ⚠️ Authentication Protection
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@@ -71,9 +71,10 @@ jobs:
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| `branch_prefix` | The prefix to use for Claude branches (defaults to 'claude/', use 'claude-' for dash format) | No | `claude/` |
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| `settings` | Claude Code settings as JSON string or path to settings JSON file | No | "" |
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| `additional_permissions` | Additional permissions to enable. Currently supports 'actions: read' for viewing workflow results | No | "" |
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| `use_commit_signing` | Enable commit signing using GitHub's commit signature verification. When false, Claude uses standard git commands | No | `false` |
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| `bot_id` | GitHub user ID to use for git operations (defaults to Claude's bot ID) | No | `41898282` |
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| `bot_name` | GitHub username to use for git operations (defaults to Claude's bot name) | No | `claude[bot]` |
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| `use_commit_signing` | Enable commit signing using GitHub's API. Simple but cannot perform complex git operations like rebasing. See [Security](./security.md#commit-signing) | No | `false` |
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| `ssh_signing_key` | SSH private key for signing commits. Enables signed commits with full git CLI support (rebasing, etc.). See [Security](./security.md#commit-signing) | No | "" |
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| `bot_id` | GitHub user ID to use for git operations (defaults to Claude's bot ID). Required with `ssh_signing_key` for verified commits | No | `41898282` |
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| `bot_name` | GitHub username to use for git operations (defaults to Claude's bot name). Required with `ssh_signing_key` for verified commits | No | `claude[bot]` |
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| `allowed_bots` | Comma-separated list of allowed bot usernames, or '\*' to allow all bots. Empty string (default) allows no bots | No | "" |
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| `allowed_non_write_users` | **⚠️ RISKY**: Comma-separated list of usernames to allow without write permissions, or '\*' for all users. Only works with `github_token` input. See [Security](./security.md) | No | "" |
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| `path_to_claude_code_executable` | Optional path to a custom Claude Code executable. Skips automatic installation. Useful for Nix, custom containers, or specialized environments | No | "" |
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