Ensure that a user (or a database was read) is used only by one application

Imagine that I have 100 users list in the database and I have 100 or more console applications that are using those users to log in somewhere. I need to use a unique user per application, I must not use the same user more than one application. How can I solve this issue, what is the best practice or pattern for that? That means a record have to read only one application/service.