If you have a login redirect loop issue on your WordPress site and recently activated a reverse proxy or a load-balancer, you need to add some constants in your wp-config.php file.
define('FORCE_SSL_ADMIN', true);
// in some setups HTTP_X_FORWARDED_PROTO might contain
// a comma-separated list e.g. http,https
// so check for https existence
if (strpos($_SERVER['HTTP_X_FORWARDED_PROTO'], 'https') !== false)
$_SERVER['HTTPS']='on';