Using Automation Secret keys into the payload

[Piyush_Annadate]

Hi, 

I've a process wherein I've to get the OAuth token, and the payload (as custom data) would be grant_type, client_id, username, password & client_secret using Content-Type as "application/x-www-form-urlencoded"

Per the current checks we want to have the payload hidden, eventually I have to use the Automation Secret Keys. 

How I can achieve the above using the Secret keys and the request type as form type content.