function verifySignedJwtWithCerts($jwt, $certs, $required_audience) { $segments = explode(".", $jwt); if (count($segments) != 3) { throw new Yoast_Google_AuthException("Wrong number of segments in token: {$jwt}"); } $signed = $segments[0] . "." . $segments[1]; $signature = Yoast_Google_Utils::urlSafeB64Decode($segments[2]); // Parse envelope. $envelope = json_decode(Yoast_Google_Utils::urlSafeB64Decode($segments[0]), true); if (!$envelope) { throw new Yoast_Google_AuthException("Can't parse token envelope: " . $segments[0]); } // Parse token $json_body = Yoast_Google_Utils::urlSafeB64Decode($segments[1]); $payload = json_decode($json_body, true); if (!$payload) { throw new Yoast_Google_AuthException("Can't parse token payload: " . $segments[1]); } // Check signature $verified = false; foreach ($certs as $keyName => $pem) { $public_key = new Yoast_Google_PemVerifier($pem); if ($public_key->verify($signed, $signature)) { $verified = true; break; } } if (!$verified) { throw new Yoast_Google_AuthException("Invalid token signature: {$jwt}"); } // Check issued-at timestamp $iat = 0; if (array_key_exists("iat", $payload)) { $iat = $payload["iat"]; } if (!$iat) { throw new Yoast_Google_AuthException("No issue time in token: {$json_body}"); } $earliest = $iat - self::CLOCK_SKEW_SECS; // Check expiration timestamp $now = time(); $exp = 0; if (array_key_exists("exp", $payload)) { $exp = $payload["exp"]; } if (!$exp) { throw new Yoast_Google_AuthException("No expiration time in token: {$json_body}"); } if ($exp >= $now + self::MAX_TOKEN_LIFETIME_SECS) { throw new Yoast_Google_AuthException("Expiration time too far in future: {$json_body}"); } $latest = $exp + self::CLOCK_SKEW_SECS; if ($now < $earliest) { throw new Yoast_Google_AuthException("Token used too early, {$now} < {$earliest}: {$json_body}"); } if ($now > $latest) { throw new Yoast_Google_AuthException("Token used too late, {$now} > {$latest}: {$json_body}"); } // TODO(beaton): check issuer field? // Check audience $aud = $payload["aud"]; if ($aud != $required_audience) { throw new Yoast_Google_AuthException("Wrong recipient, {$aud} != {$required_audience}: {$json_body}"); } // All good. return new Yoast_Google_LoginTicket($envelope, $payload); }