User-defined security zones allow users to configure multiple security zones and share them between routing instances. This allows users to easily manage multiple security zones and their associated policies. For example, a user can create a security zone for corporate traffic, a security zone for guest traffic, and a security zone for public traffic, and then configure policies to control the flow of traffic between each of these security zones. Transit traffic can also be managed using user-defined security zones, as the policies applied to these zones will be applied to the transit traffic as well.

The correct command to collect the serial number of an SRX Series device is the show chassis hardware command [1]. This command will return the serial number of the device, along with other information about the device such as the model number, part number, and version.
This command is available in Junos OS. More information about the show chassis hardware command can be found in the Juniper Networks technical documentation here [1]: https://www.juniper.net/documentation/en_US/junos/topics/reference/command-summary/show-chassis-hardware.html.

"Local Authentication-In local authentication, the SRX Series device validates the user credentials by checking them in the local database. In this method, the administrator handles change of password or resetting of forgotten password. Here, it requires that an user must remember a new password. This option is not much preferred from a security standpoint.
* External Authentication-In external authentication, you can allow the users to use the same user credentials they use when accessing other resources on the network. In many cases, user credentials are domain logon used for Active Directory or any other LDAP authorization system. This method simplifies user experience and improves the organization's security posture; because you can maintain the authorization system with the regular security policy used by your organization."
https://www.juniper.net/documentation/us/en/software/secure-connect/secure-connect-administrator-guide/topics/topic-map/secure-connect-getting-started.html