There are two methods to add authentication and both are done on the ISR (router) and are very simple.

1.  Create a username and password on the router.  

Example:  

config t

username brett password 0 pass123

end

copy run start

2.  Follow step A or B.

A.  config t

        aaa new-model

     end

     copy run start

B*.  config t

       line 66

       login local

      end

copy run start

3.  Now session into the service module and you will see a request for the username and password.

*   Step B relies on knowing ISR and Service module communication line.  You can get this information via the following steps.

1.  Session into the service module.

2.  Exit back to the router by typing Ctl + Shift + 6, then type x

3.   Type 'show users'.  The data showing Line: tty, Host: incoming is the communication line.

4.   You can return to the service module by pressing the <Enter> key.