Hi All,
Have found a workaround. Steps to follow are:
1) We need 2 REST steps:
a) First REST calls will get the access token using the Outh2.0 REST call and username and password and also the parameter as grant_type = client_credentials.
b) Access Token received in the first call can be saved in a property to be used in the actual REST call that service has to make.
For more information, please visit this link, this article only gave the idea of following the above steps:
https://stormpath.com/blog/build-api-restify-stormpath
Attaching the screen shot of the REST STEP for ACCESS TOKEN.