Beginning with Citrix Provisioning Services 5.1, Citrix introduced a feature that required an end user to enter credentials to fully boot a target device. My assumption is that this would be primarily for Physical Workstations booting images via PVS in a XenDesktop scenario. (i.e. Localized GotoMyPC type solutions). For Hosted Desktops and obviously Servers, this feature is not needed and often times, troublesome if enabled.
When the target device is booted, it will sit at the prompt to the left until a valid Domain\Username is entered. By default, no password is required but that could also be set on the device itself. Not good for unattended reboots of servers.
To disable this feature, check the properties of your Collection and uncheck ‘Enable user login to devices’ from the options tab.
Unchecking the option allows the Target device to boot without intervention and has absolutely no impact on user’s ability to actually log into the booted device. (i.e. Windows)