Chief-Assistant Function

In my company, we want to do something like a Chief Assistance funkction, which means, if someon calls the extension of the boss, his assistant will get the call and decides wheather its forwarded or not. So far so simple.
What we want to do is that anyone can call the extension 100 followed by the number which is the target of the forwarding (on the Boss phone). The phone where the calls are forwarded to should be the only one which is able to call the number of the boss phone.
Any suggestions?

Restricting directly calling the boss is simply done with contexts. I’m not clear how the assistant receives the information as to which boss was called.

Hi, Thanks for the reply.
Normally, one assistant per boss. But we want to implement the function for everyone, So that we don’t have to mess in the code everytime.

Anyone else here knowing somehing about this topic?