Signing of pixhawk with Certificate of authenticity

How to sign of pixhawk with COA in ardupilot Arducopter 3.6.7 stable version with ChibiOS RTOS. we are drone manufacturing in India.we want to customized ardupilot and mission planner both so that only our customized mission planner talk to customized firmware.Please suggest the solution.

It is not a good idea, but if you customize MP and AP code, then you have the capability to do an identification message during connecting.

I am talking about this link:
So, my question is what is alternative for nsh if i am using Chibios RTOS based Ardupilot.

The Auth command is to identify the boards as Authentic.
It doesn’t refer to communication from a GCS.
What you are looking for is Mavlink 2.0 signing.

I am looking for signing for my custom data with SHA256withRSA (2048 bit key) digital signing scheme by Mavlink 2.0 signing so my question is this possible with Mavlink 2.0.