Edgar
You don't need to buy additional products, you can do it all in DataFlex, which is what this sub-forum is all about.
The cHttpTransfer class, or the cJsonHttpTransfer class, will do what is required for actually consuming RESTful APIs.
For dealing with authentication, there are other classes here that will help with that as well. There are copious examples for using OAuth 2.0, for instance. For Basic Authentication ("Basic Auth"), you only need to set the psUserName and psPassword properties of the two classes above.
Mike