Web App that handle users directly with the database

I am looking for examples or approaches of how I could use a web application in Java (Spring would be ideal) to do all the connection and validation directly with the Oracle database engine, that means, not having a user table in the application where it is stored the username and password, instead use the Oracle connection pool to validate the user (username and password) and connect the application with those credentials when the user provides them.

The reason is because the company has a CRM with Oracle products and performs all its administration of users and permissions (with database roles) directly with Oracle and it is required to extend certain CRM functionalities without changing this user management scheme.

In the examples I found about Spring, a user and password are always defined in a property file in a static way.

Any advice or guidance on what approach can I take to accomplish this?