azure-storage-common/src/Common/Internal/Utilities.php
public static function calculateContentMD5($content)
    {
        Validate::notNull($content, 'content');
        Validate::canCastAsString($content, 'content');

        return base64_encode(md5($content, true));
    }
public static function calculateContentMD5($content)
    {
        Validate::notNull($content, 'content');
        Validate::canCastAsString($content, 'content');

        return base64_encode(md5($content, true));
    }
Calculates the content MD5 which is base64 encoded. This should be align
with the server calculated MD5.

@param  string $content the content to be calculated.

@return string