base64url encoding for hmac function

[irina-gherman-d]

Having this piece of code,

    <AssignVariable>
        <Name>hmac.computed_base64</Name>
        <Template>{hmacSha256(private.hmacSecretKey,hmac.stringToSign,'utf-8','base64')}</Template>
    </AssignVariable>

how can i get this base64URL encoded, and not simple base64 encoded?