Strategy for integrating multiple APIs for multi-tenant application

Can anyone suggest best way for implementing the below scenario.

 

In a multitenant application where we are tied up with different vendors, based on the logged in user we need to dynamically connect to a vendor's API and fetch user information. What is the best way to design the scenario so that in future if we tie up with a new vendor we need to make minimum changes to our code to call his APIs. What are the pitfalls to be considered in such scenarios. Any pointers to any existing pattern/practice for such implementation would help a lot.