azure-storage-common/src/Common/Internal/Utilities.php
public static function isoDate(\DateTimeInterface $date)
    {
        $date = clone $date;
        $date = $date->setTimezone(new \DateTimeZone('UTC'));

        return str_replace('+00:00', 'Z', $date->format('c'));
    }
public static function isoDate(\DateTimeInterface $date)
    {
        $date = clone $date;
        $date = $date->setTimezone(new \DateTimeZone('UTC'));

        return str_replace('+00:00', 'Z', $date->format('c'));
    }
Generate ISO 8601 compliant date string in UTC time zone

@param \DateTimeInterface $date The date value to convert

@return string