Entry points to one location from different products

The scenario

We have one Product that contains a Candidate list in one location in our main database, with its own UI and functionality (standard list admin functionality)

We also have about six different individual internal branded websites/products under our network, but all accessing this main database

User story: As a user of one of these products, I want to be able to gain access/easily add to or create a new candidate list from any of our products UI that i am using, instead of having to log out of whatever product im currently using, and log into this candidate list to perform this action.

So in essence - Have the functionality of the candidate list but retain the look and feel of the product i'm currently using

What do you guys think would be the best approach for this? i was thinking this would could be achieved by a pop up window/Modal window and following a step through process

Or is it best to develop the UI and call an API for this?

Hope this is clear?