If you want to let a user connect to your eVouala instance, you will need to activate the Database Access. Follow those steps to activate this option on a user:
1) Click on Advance - Users in the main menu
2) Select a user and click on Edit User button
3) Check Database Access option
4) Set a Password
This user will be able to connect to the PostGIS database engine of your instance with his eVouala user/pw credential. Note that the user will not be able to change his password.