Tableau Server's repository is configured for username/password authentication only. The users viewing workbooks would have to be viewing them as the "readonly" or "tableau" user. Their own user accounts don't exist as users on the Tableau Server repository, so they couldn't access it using integrated auth, even if it were turned on.
This page in the product help details which of these two accounts to use, depending on the tables you need to access:
You'll want to either extract the data, or embed the credentials from one of these accounts into the data source in order to give users access to the information.