feat(signature): resolve author via Commits API before email search

README.md

@@ -77,8 +77,8 @@ Available checks:
 * `imperative` - First word is an imperative verb (for example `add` not `added`)
 * `body` - Blank line separates subject from body, and body is non-empty
 * `signed-off` - `Signed-off-by:` trailer exists
-* `signature` - Verify GPG or SSH signature via GitHub public key lookup, with
-    fallback to `git verify-commit`
+* `signature` - Verify GPG or SSH signature via the GitHub Commits API or
+    public key lookup
 
 ### Subject length
 
@@ -202,20 +202,27 @@ independently of `--enable`/`--disable`.
 
 ### Signature verification
 
-The `signature` check tries to verify the commit without any local keyring setup:
+The `signature` check verifies the commit without any local keyring setup:
 
-1. Look up the commit author's email in the GitHub API to find their GitHub
-   username.
-2. Fetch their public keys from `github.com/{username}.gpg` and
+1. If the repo has a GitHub remote, call the Commits API
+   (`GET /repos/{owner}/{repo}/commits/{sha}`) to resolve the author's GitHub
+   username — this works for corporate emails, noreply addresses, or any email
+   not listed publicly on a GitHub profile.
+2. If the Commits API is unavailable (no GitHub remote, commit not yet pushed,
+   or API error), fall back to searching GitHub by the commit author's email.
+3. Fetch the resolved user's public keys from `github.com/{username}.gpg` and
    `github.com/{username}.keys`.
-3. Try GPG verification: import the fetched key into a temporary keyring and
+4. Try GPG verification: import the fetched key into a temporary keyring and
    run `git verify-commit`.
-4. Try SSH verification: write a temporary `allowed_signers` file and run
+5. Try SSH verification: write a temporary `allowed_signers` file and run
    `git verify-commit` with the SSH allowed-signers config.
-5. If any key verifies, the check passes. If none do, it fails.
+6. If any key verifies, the check passes. If none do, it fails.
 
-If the author's email is not found on GitHub, or the API is unreachable, the
-check fails with a clear error — there is no silent fallback.
+If the author cannot be resolved via either method, or the GitHub API is
+unreachable, the check fails with a clear error.
+
+For private repositories, set `GITHUB_TOKEN` or `GH_TOKEN` so the Commits API
+can authenticate.
 
 ### Configuration file
 
@@ -251,9 +258,11 @@ full precedence and ignore config file values when provided.
 
 ### Environment variables
 
-| Variable                   | Default | Description                                  |
-| -------------------------- | ------- | -------------------------------------------- |
-| `COMMIT_GUARD_GIT_TIMEOUT` | `10`    | Timeout in seconds for git subprocess calls. |
+| Variable                   | Default | Description                                                               |
+| -------------------------- | ------- | ------------------------------------------------------------------------- |
+| `COMMIT_GUARD_GIT_TIMEOUT` | `10`    | Timeout in seconds for git subprocess calls.                              |
+| `GITHUB_TOKEN`             | —       | GitHub token for Commits API access on private repos (signature check).   |
+| `GH_TOKEN`                 | —       | Alias for `GITHUB_TOKEN`; used when `GITHUB_TOKEN` is not set.            |
 
 ```bash
 COMMIT_GUARD_GIT_TIMEOUT=30 commit-guard --range origin/main..HEAD

docs/index.html

@@ -377,7 +377,7 @@ <h3>Checks</h3>
               </tr>
               <tr>
                 <td><code>signature</code></td>
-                <td>GPG or SSH signature is valid — verified via GitHub public key lookup</td>
+                <td>GPG or SSH signature is valid — verified via GitHub Commits API or public key lookup</td>
               </tr>
             </tbody>
           </table>
@@ -432,15 +432,25 @@ <h3>Signature verification</h3>
           pre-configured local keyring:
         </p>
         <ol>
-          <li>Look up the commit author's email via the GitHub search API to find their username.</li>
-          <li>Fetch their public keys from <code>github.com/{username}.gpg</code> and <code>github.com/{username}.keys</code>.</li>
+          <li>If the repo has a GitHub remote, call the Commits API
+            (<code>GET /repos/{owner}/{repo}/commits/{sha}</code>) to resolve
+            the author's GitHub username — works for corporate emails, noreply
+            addresses, or any email not listed publicly on a GitHub profile.</li>
+          <li>If the Commits API is unavailable (no GitHub remote, commit not
+            yet pushed, or API error), fall back to searching GitHub by the
+            commit author's email.</li>
+          <li>Fetch the resolved user's public keys from
+            <code>github.com/{username}.gpg</code> and
+            <code>github.com/{username}.keys</code>.</li>
           <li>Try GPG verification using a temporary keyring.</li>
           <li>Try SSH verification using a temporary <code>allowed_signers</code> file.</li>
           <li>Pass if any key verifies; fail if none do.</li>
         </ol>
         <p>
-          If the author's email is not found on GitHub, or the API is
-          unreachable, the check fails with a clear error. Disable the
+          If the author cannot be resolved via either method, or the GitHub API
+          is unreachable, the check fails with a clear error. For private
+          repositories, set <code>GITHUB_TOKEN</code> or <code>GH_TOKEN</code>
+          so the Commits API can authenticate. Disable the
           <code>signature</code> check if GitHub API access is unavailable:
         </p>
         <pre><code class="language-bash">commit-guard --disable signature</code></pre>
@@ -470,6 +480,16 @@ <h3>Environment variables</h3>
                 <td><code>10</code></td>
                 <td>Timeout in seconds for git subprocess calls</td>
               </tr>
+              <tr>
+                <td><code>GITHUB_TOKEN</code></td>
+                <td>—</td>
+                <td>GitHub token for Commits API access on private repos (signature check)</td>
+              </tr>
+              <tr>
+                <td><code>GH_TOKEN</code></td>
+                <td>—</td>
+                <td>Alias for <code>GITHUB_TOKEN</code>; used when <code>GITHUB_TOKEN</code> is not set</td>
+              </tr>
             </tbody>
           </table>
         </figure>

src/git_commit_guard/__init__.py

@@ -34,6 +34,9 @@
 
 _NON_IMPERATIVE_SUFFIX_RE = re.compile(r"(?:ing|ed)$")
 _TRAILER_RE = re.compile(r"^[\w-]+:\s+\S")
+_GITHUB_REMOTE_RE = re.compile(
+    r"github\.com[:/](?P<owner>[^/]+)/(?P<repo>[^/\s]+?)(?:\.git)?$"
+)
 
 SUBJECT_RE = re.compile(
     r"^(?P<type>\w+)(?:\((?P<scope>[^)]+)\))?!?:\s+(?P<desc>.+)$",
@@ -268,6 +271,35 @@ def _get_author_email(rev):
     ).strip()
 
 
+def _get_github_remote_info():
+    try:
+        url = subprocess.check_output(
+            ["git", "remote", "get-url", "origin"],  # noqa: S607 Starting a process with a partial executable path
+            text=True,
+            stderr=subprocess.PIPE,
+            timeout=_git_timeout(),
+        ).strip()
+    except subprocess.CalledProcessError:
+        return None
+    match = _GITHUB_REMOTE_RE.search(url)
+    if not match:
+        return None
+    return match.group("owner"), match.group("repo")
+
+
+def _fetch_github_commit_author(owner, repo, sha):
+    url = f"https://api.github.com/repos/{owner}/{repo}/commits/{sha}"
+    headers = {"Accept": "application/vnd.github+json"}
+    token = os.environ.get("GITHUB_TOKEN") or os.environ.get("GH_TOKEN")
+    if token:
+        headers["Authorization"] = f"Bearer {token}"
+    req = urllib.request.Request(url, headers=headers)  # noqa: S310 Audit URL open for permitted schemes
+    with urllib.request.urlopen(req, timeout=_git_timeout()) as resp:  # noqa: S310 Audit URL open for permitted schemes
+        data = json.loads(resp.read())
+    author = data.get("author")
+    return author["login"] if author else None
+
+
 def _fetch_github_username(email):
     url = f"https://api.github.com/search/users?q={email}+in:email"
     req = urllib.request.Request(url, headers={"Accept": "application/vnd.github+json"})  # noqa: S310 Audit URL open for permitted schemes
@@ -347,7 +379,14 @@ def _verify_ssh(rev, email, ssh_text):
 def check_signature(rev, result):
     try:
         email = _get_author_email(rev)
-        username = _fetch_github_username(email)
+        username = None
+        remote = _get_github_remote_info()
+        if remote:
+            owner, repo = remote
+            with contextlib.suppress(urllib.error.URLError, TimeoutError):
+                username = _fetch_github_commit_author(owner, repo, rev)
+        if username is None:
+            username = _fetch_github_username(email)
         if username is None:
             result.error(
                 "commit author not found on GitHub — cannot verify signature",