How to create a gateway between your router and the internet that can terminate ssl at the gateway?

How to create a gateway between your router and the internet that can
terminate ssl at the gateway?

I have a buffalo router (N600). I want to create a program that inspect
and possible modify the traffic going through my router. My program needs
to terminate SSL traffic as well so it can read SSL traffic. Is there a
similar software that already exists? Where this program should live :
between my computer and my router or as a gateway between my router and
the internet?
Thanks,
Sean