Hi Utsa Das,
The hassle of getting token and using in next steps is eliminated by RIH(via App Connectors/HTTP Connector).
For Reltio you can have Reltio Connector and use Custom API without need of token for others you can use HTTP Connector with appropriate credentials like OAuth, Username password, Client credentials etc.
Just wanted to understand the next step after you get TOKEN as you will be calling an Reltio Custom API and that can be achieved by Custom Action of Reltio Connector.
So, there is no need to get Token and use in further steps at least for Reltio API’s.