Execute and lock a user into a program upon login

[Steve Bertrand]

Hi everyone,

Although the application of my question focuses on network operation, I
believe that the objective fits this list.

Mostly irrelevant, I have been working on securing my network perimeter.
I have a FreeBSD box that acts as a host-based BGP peer to all edge
connected routers.

I use this host-based Quagga FBSD router to distribute routes that are
to be blackholed by the edge devices.

What I want is to set up an environment so that when a specific user
logs in to the box via SSH, a command is run, and they immediately get
dropped into the environment that the command produces.

When they exit this 'command', the login session is dropped.

Essentially, I want to 'lock' a user into a program upon SSH login, and
drop them from the SSH session when the program terminates.

In essence:

- user 'router' connects via SSH
- user is dropped into the application 'vtysh'
- user performs operations
- user exits from program
- shell drops (ie. user does not have to exit the csh shell to drop the
SSH connection)

Steve