Create a "show_per_user" column in external_sys to indicate if users are able to provide credentials for this external system. Create a "test_expr" column in external_sys to hold the expression that will be used to test the connection to an external system. Create table to hold the plugins that are allowed to access each external system FK from external_sys_plugins.external_sys_id to external_sys.id. Index for external_sys_plugins.external_sys_id.