eZ Publish sessions are handled by the Symfony stack, through session handlers. As en example, in order to store your session data in a database, you may use the PdoSessionHandler:

framework:
    session:
        # ...
        handler_id:     session.handler.pdo

parameters:
    pdo.db_options:
        db_table:    session
        db_id_col:   session_id
        db_data_col: session_value
        db_time_col: session_time

services:
    pdo:
        class: PDO
        arguments:
            dsn:      "mysql:dbname=<mysql_database>"
            user:     <mysql_user>
            password: <mysql_password>

    session.handler.pdo:
        class:     Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler
        arguments: ["@pdo", "%pdo.db_options%"]

For more information on this and other included handlers, or information on developing your own, please check the online Symfony documentation.

To configure sessions in your eZ Publish 5 setup, look to the documentation of Symfony HTTP Fundation component.