Basics to integrate
Tellus will be accessible for you as a REST-ful API.
You can access the Swagger explorer of the API. To find the API address go to Services in Forma, select the Instance you'd like to access and click Root Address. In the url add an extra "/docs".
Since the API is REST based, you can integrate from any modern programming language.
It is advised to create your own set of User interfaces with your own branding for Proof of Concepts, Prototypes, or production projects.
Using another user
To use another user, whether, through the Testing UI or the API, you would need to create a new instance like is explained here.
Be sure to use the new address for that user as shown here Services in Forma.