In case of a LoRaWAN® OTAA activation request, ChirpStack Network Server will call the Join Server configured in the Configuration file which will handle the authentication of the device and the generation of the session-keys. The Join Server API is specified by the LoRaWAN Backend Interfaces specification. By default ChirpStack Application Server fulfils this role.
In case of a LoRaWAN ABP devices, ChirpStack Network Server has support for pre-activating devices through its API. Once activated, ChirpStack Network Server will handle the device in exactly the same way as an OTAA activated device.