github-callback.html

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width,initial-scale=1">
  <title>GitHub Sign-In</title>
  <style>html,body{margin:0;width:100%;height:100%;background:#111;color:#eee;font:14px system-ui,sans-serif;display:grid;place-items:center}main{text-align:center;opacity:.8}</style>
</head>
<body>
<main>Completing GitHub sign-in…</main>
<script>
(function(){
  const params = new URLSearchParams(location.search);
  const payload = {
    type: 'github-oauth-callback',
    code: params.get('code'),
    state: params.get('state'),
    error: params.get('error'),
    errorDescription: params.get('error_description') || ''
  };

  if (window.opener && window.opener !== window) {
    try {
      window.opener.postMessage(payload, location.origin);
    } catch (_) {}
    setTimeout(() => window.close(), 100);
    return;
  }

  // Popup blockers can force the original window to navigate through OAuth.
  // Return to the editor URL recorded by github.js and preserve the callback.
  let returnUri = '';
  try {
    const pending = JSON.parse(localStorage.getItem('editor.github.oauth.pending') || 'null');
    returnUri = String(pending?.returnUri || '');
  } catch (_) {}

  try {
    const target = new URL(returnUri || location.href);
    if (target.origin !== location.origin) throw new Error('invalid callback target');
    target.search = '';
    target.hash = '';
    for (const key of ['code','state','error','error_description']) {
      const value = params.get(key);
      if (value) target.searchParams.set(key, value);
    }
    location.replace(target.href);
  } catch (_) {
    document.querySelector('main').textContent = 'GitHub sign-in completed. Return to the editor to continue.';
  }
})();
</script>
</body>
</html>