Official documentation for UniFi adoption methods

Layer 2 Adoption

UniFi adopts devices within the layer 2 network via an SSH remote command to assign the authkey used for inform encryption. The controller will send /usr/bin/ set-adopt <inform_url> <authkey> to the device using the default username and password of ubnt:ubnt.

Layer 3 Adoption

Layer 3 adoption works by having a new device reach out with an inform packet to a 'remote' controller over HTTP POST using the default authkey. The new device will show as Pending Adoption in the UniFi controller UI until an operator adopts the device.

Adoption Process

On the first inform packet during adoption the controller will respond with a setparam command that will set the device's unique authkey as well as other config settings. The second response will provision the device and contain the device's configuration.