ソーシャルログインのセットアップ

// npm install firebase-admin
import admin from 'firebase-admin';
admin.initializeApp({ credential: admin.credential.applicationDefault() });

app.post('/api/auth/social', async (req, res) => {
  const { provider, uid, idToken, email, displayName } = req.body;

  // Google および Apple の Firebase ID Token を検証
  if (idToken) {
    const decoded = await admin.auth().verifyIdToken(idToken);
    if (decoded.uid !== uid) return res.status(401).json({ error: 'UID mismatch' });
  }

  // uid でユーザーを検索または作成
  let user = await db.users.findOne({ socialProvider: provider, socialId: uid });
  if (!user) {
    user = await db.users.create({ socialProvider: provider, socialId: uid, email, name: displayName });
  }

  req.session.userId = user.id;
  res.json({ ok: true, user: { id: user.id, name: user.name } });
});

// NuGet: FirebaseAdmin
using FirebaseAdmin;
using FirebaseAdmin.Auth;

[HttpPost("auth/social")]
public async Task<IActionResult> SocialLogin([FromBody] SocialLoginRequest request)
{
    // Google および Apple の Firebase ID Token を検証
    if (!string.IsNullOrEmpty(request.IdToken))
    {
        var decoded = await FirebaseAuth.DefaultInstance.VerifyIdTokenAsync(request.IdToken);
        if (decoded.Uid != request.Uid)
            return Unauthorized(new { error = "UID mismatch" });
    }

    var user = await _userService.FindOrCreateBySocialAsync(
        request.Provider, request.Uid, request.Email, request.DisplayName);

    HttpContext.Session.SetInt32("UserId", user.Id);
    return Ok(new { ok = true, user = new { user.Id, user.Name } });
}

// Maven: com.google.firebase:firebase-admin
@PostMapping("/api/auth/social")
public ResponseEntity<?> socialLogin(@RequestBody SocialLoginRequest request,
                                      HttpSession session) throws FirebaseAuthException {
    // Google および Apple の Firebase ID Token を検証
    if (request.getIdToken() != null) {
        FirebaseToken decoded = FirebaseAuth.getInstance().verifyIdToken(request.getIdToken());
        if (!decoded.getUid().equals(request.getUid()))
            return ResponseEntity.status(401).body(Map.of("error", "UID mismatch"));
    }

    User user = userService.findOrCreateBySocial(
        request.getProvider(), request.getUid(), request.getEmail(), request.getDisplayName());
    session.setAttribute("userId", user.getId());
    return ResponseEntity.ok(Map.of("ok", true, "userId", user.getId()));
}

<?php
// composer require kreait/firebase-php
use Kreait\Firebase\Factory;

$data = json_decode(file_get_contents('php://input'), true);
$provider    = $data['provider'];
$uid         = $data['uid'];
$idToken     = $data['idToken'] ?? null;
$email       = $data['email'] ?? null;
$displayName = $data['displayName'] ?? null;

// Google および Apple の Firebase ID Token を検証
if ($idToken) {
    $firebase = (new Factory)->withServiceAccount('/path/to/serviceAccount.json');
    $auth = $firebase->createAuth();
    $decoded = $auth->verifyIdToken($idToken);
    if ($decoded->claims()->get('sub') !== $uid) {
        http_response_code(401);
        echo json_encode(['error' => 'UID mismatch']);
        exit;
    }
}

$stmt = $pdo->prepare('SELECT * FROM users WHERE social_provider = ? AND social_id = ?');
$stmt->execute([$provider, $uid]);
$user = $stmt->fetch();

if (!$user) {
    $pdo->prepare('INSERT INTO users (social_provider, social_id, email, name) VALUES (?, ?, ?, ?)')
        ->execute([$provider, $uid, $email, $displayName]);
    $userId = $pdo->lastInsertId();
} else {
    $userId = $user['id'];
}

$_SESSION['user_id'] = $userId;
echo json_encode(['ok' => true, 'userId' => $userId]);