Thanks for all your input. I took time to check with the provider to see if they offer any alternatives for authentication and unfortunately they done. So I have to go with implementing the UDF to code the signature as dynamic attribute and use it in the URL pattern as Indrajit suggested. Their authentication is done at the URL when the API call is made with the payload as the request query as JSON.
Will update once I have this implemented successfully.
Thanks again for all the input.
Larry.