HMAC SHA1 Signature for google

Hi,

I need to build a google signature using HMAC SHA1 and find a way to do it on our WAS 6.20 system

You can see the google explaination underhttp://code.google.com/apis/maps/documentation/premier/guide.html#URLSigning.

I Beleive I can use FM SSFC_BASE64_ENCODE and SSFC_BASE64_DECODE to do the base64 parts.

However, I don't know how to do the HMAC SHA1 part.

We don't have FM's like CALCULATE_HMAC_FOR_RAW in our system so I think I'll have to create a new FM but I have no idea how to build this.

Any ideas?