Incorrect time string when system timezone is not GMT

[jaclam1]

cybersource-rest-client-php/lib/Authentication/Jwt/JsonWebTokenGenerator.php

Line 31 in a9ddad7

$date = date("D, d M Y G:i:s ").GlobalParameter::GMT;

When system time zone is not GMT, this line will return the local time string and attach a GMT suffix behind. API call will fail with "UNAUTHORIZED_USER" because of the "iat" field in JWT payload different from current time too much.