This read-write DisplayString is the shared secret used between the AAA client and server, intended to be set only when the AAA traffic itself travels through a VPN tunnel, and it always reads back as an empty string for security. An admin writes this to establish a trust key with the RADIUS server, then relies on the empty read-back to confirm the value can't be retrieved after the fact. For example, after configuring the shared secret for a branch office's RADIUS profile, an admin verifying the setup would see a blank value returned and instead confirm success by testing an actual authentication attempt.