When using connection_configurations on ems_container default authentication is nil, because the connection_configuration_by_role method does not respect the authentication default type.
https://github.com/ManageIQ/manageiq/pull/9845
Verified on 5.7.0.12-rc2. Here is the output: irb(main):008:0* ExtManagementSystem.first.connection_configuration_by_role("default").authentication.authtype PostgreSQLAdapter#log_after_checkout, connection_pool: size: 5, connections: 1, in use: 1, waiting_in_queue: 0 => "bearer"