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<?php
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defined('BASEPATH') or exit('No direct script access allowed');
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/**
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* Firebase Auth helper – verify Firebase ID tokens (JWT) for API auth.
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* Complies with Firebase Auth process: clients can send "Authorization: Bearer <id_token>"
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* and the backend verifies the token with Google's public keys.
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* Uses FCM_PROJECT_ID (or FIREBASE_PROJECT_ID) for aud/iss validation.
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*/
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if (!function_exists('firebase_auth_get_bearer_token')) {
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/**
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* Get Bearer token from Authorization header.
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*
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* @return string|null Token or null if missing/invalid
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*/
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function firebase_auth_get_bearer_token()
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{
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$auth = isset($_SERVER['HTTP_AUTHORIZATION']) ? $_SERVER['HTTP_AUTHORIZATION'] : '';
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if ($auth === '' && function_exists('apache_request_headers')) {
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$headers = apache_request_headers();
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$auth = isset($headers['Authorization']) ? $headers['Authorization'] : (isset($headers['authorization']) ? $headers['authorization'] : '');
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}
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if (preg_match('/^\s*Bearer\s+(\S+)\s*$/i', $auth, $m)) {
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return $m[1];
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}
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return null;
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}
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}
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if (!function_exists('firebase_auth_base64url_decode')) {
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function firebase_auth_base64url_decode($data)
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{
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$pad = 4 - (strlen($data) % 4);
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if ($pad !== 4) {
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$data .= str_repeat('=', $pad);
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}
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return base64_decode(strtr($data, '-_', '+/'));
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}
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}
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if (!function_exists('firebase_auth_fetch_google_jwks')) {
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/**
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* Fetch and cache Firebase Auth public keys (JWK set).
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*
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* @return array|null JWK set array or null on failure
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*/
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function firebase_auth_fetch_google_jwks()
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{
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$cache_key = 'firebase_auth_jwks';
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$cache_ttl = 3600;
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if (function_exists('get_instance')) {
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$ci = &get_instance();
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if (isset($ci->cache) && method_exists($ci->cache, 'get')) {
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$cached = $ci->cache->get($cache_key);
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if ($cached !== false) {
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return $cached;
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}
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}
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}
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$url = 'https://www.googleapis.com/service_accounts/v1/jwk/securetoken@system.gserviceaccount.com';
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$ctx = stream_context_create(array('http' => array('timeout' => 10)));
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$raw = @file_get_contents($url, false, $ctx);
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if ($raw === false) {
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log_message('error', 'Firebase Auth: Failed to fetch JWKs');
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return null;
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}
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$jwks = json_decode($raw, true);
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if (empty($jwks['keys'])) {
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log_message('error', 'Firebase Auth: Invalid JWKs response');
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return null;
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}
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if (function_exists('get_instance')) {
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$ci = &get_instance();
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if (isset($ci->cache) && method_exists($ci->cache, 'save')) {
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$ci->cache->save($cache_key, $jwks, $cache_ttl);
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}
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}
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return $jwks;
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}
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}
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if (!function_exists('firebase_auth_jwk_to_pem')) {
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/**
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* Convert JWK (RSA n,e) to PEM for openssl.
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*
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* @param array $jwk JWK with kty RSA, n, e
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* @return string|false PEM or false
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*/
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function firebase_auth_jwk_to_pem($jwk)
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{
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if (empty($jwk['n']) || empty($jwk['e']) || (isset($jwk['kty']) && $jwk['kty'] !== 'RSA')) {
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return false;
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}
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$n = firebase_auth_base64url_decode($jwk['n']);
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$e = firebase_auth_base64url_decode($jwk['e']);
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if ($n === false || $e === false) {
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return false;
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}
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$rsa = array(
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'n' => $n,
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'e' => $e,
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);
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$der = firebase_auth_build_rsa_der($rsa);
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if ($der === false) {
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return false;
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}
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$pem = "-----BEGIN PUBLIC KEY-----\n" . chunk_split(base64_encode($der), 64, "\n") . "-----END PUBLIC KEY-----";
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return $pem;
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}
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}
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if (!function_exists('firebase_auth_build_rsa_der')) {
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function firebase_auth_build_rsa_der($rsa)
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{
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$n = $rsa['n'];
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$e = $rsa['e'];
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$n_len = strlen($n);
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$e_len = strlen($e);
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if ($n[0] & "\x80") {
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$n_len++;
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}
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if ($e[0] & "\x80") {
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$e_len++;
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}
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$seq = "\x02" . chr($e_len) . ($e[0] & "\x80" ? "\0" : '') . $e
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. "\x02" . chr($n_len) . ($n[0] & "\x80" ? "\0" : '') . $n;
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$bit_string = "\x03" . chr(strlen($seq) + 1) . "\x00" . $seq;
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$oid = "\x06\x09\x2a\x86\x48\x86\xf7\x0d\x01\x01\x01\x05\x00";
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$inner = "\x30" . firebase_auth_der_len(strlen($bit_string) + strlen($oid)) . $bit_string . $oid;
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$outer = "\x30" . firebase_auth_der_len(strlen($inner)) . $inner;
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return $outer;
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}
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}
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if (!function_exists('firebase_auth_der_len')) {
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function firebase_auth_der_len($len)
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{
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if ($len < 128) {
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return chr($len);
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}
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$buf = '';
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while ($len > 0) {
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$buf = chr($len & 0xff) . $buf;
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$len >>= 8;
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}
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return chr(0x80 | strlen($buf)) . $buf;
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}
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}
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if (!function_exists('firebase_auth_verify_id_token')) {
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/**
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* Verify a Firebase ID token (JWT) and return decoded payload.
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*
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* @param string $id_token The JWT string
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* @param string|null $project_id Firebase project ID (default: FCM_PROJECT_ID or FIREBASE_PROJECT_ID constant)
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* @return array|null Payload (uid, email, etc.) or null if invalid
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*/
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function firebase_auth_verify_id_token($id_token, $project_id = null)
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{
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if (!is_string($id_token) || $id_token === '') {
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return null;
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}
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$parts = explode('.', $id_token);
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if (count($parts) !== 3) {
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return null;
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}
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$header = json_decode(firebase_auth_base64url_decode($parts[0]), true);
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$payload = json_decode(firebase_auth_base64url_decode($parts[1]), true);
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if (!$header || !$payload) {
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log_message('debug', 'Firebase Auth: Invalid JWT decode');
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return null;
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}
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if ($project_id === null || $project_id === '') {
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if (defined('FCM_PROJECT_ID') && FCM_PROJECT_ID !== '') {
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$project_id = FCM_PROJECT_ID;
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} elseif (defined('FIREBASE_PROJECT_ID') && FIREBASE_PROJECT_ID !== '') {
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$project_id = FIREBASE_PROJECT_ID;
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} else {
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$project_id = '';
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}
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}
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if ($project_id === '') {
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log_message('error', 'Firebase Auth: FCM_PROJECT_ID not set');
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return null;
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}
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$expected_iss = 'https://securetoken.google.com/' . $project_id;
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if (empty($payload['iss']) || $payload['iss'] !== $expected_iss) {
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log_message('debug', 'Firebase Auth: iss mismatch');
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return null;
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}
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if (empty($payload['aud']) || $payload['aud'] !== $project_id) {
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log_message('debug', 'Firebase Auth: aud mismatch');
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return null;
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}
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if (empty($payload['exp']) || (int) $payload['exp'] < time()) {
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log_message('debug', 'Firebase Auth: token expired');
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return null;
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}
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$jwks = firebase_auth_fetch_google_jwks();
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if (!$jwks) {
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return null;
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}
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$kid = isset($header['kid']) ? $header['kid'] : null;
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$key = null;
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foreach ($jwks['keys'] as $k) {
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if (isset($k['kid']) && $k['kid'] === $kid) {
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$key = $k;
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break;
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}
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}
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if (!$key) {
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$key = $jwks['keys'][0];
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}
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$pem = firebase_auth_jwk_to_pem($key);
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if (!$pem) {
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return null;
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}
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$pub = openssl_pkey_get_public($pem);
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if ($pub === false) {
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return null;
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}
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$payload_to_verify = $parts[0] . '.' . $parts[1];
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$sig_raw = firebase_auth_base64url_decode($parts[2]);
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if ($sig_raw === false) {
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openssl_free_key($pub);
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return null;
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}
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$ok = openssl_verify($payload_to_verify, $sig_raw, $pub, OPENSSL_ALGO_SHA256);
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openssl_free_key($pub);
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if ($ok !== 1) {
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log_message('debug', 'Firebase Auth: signature verification failed');
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return null;
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}
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return $payload;
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}
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}
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