Help with 'expect'

hi guys I am in need for some 'expect' scripting help

I have the following bash script and need to make this automated using the same password everytime (since i am configuring different deviced everytime, I can not use SSH Key for this)

Can anyone tell me how to integrate the 'expect' usages into this script so that MySecrectPass will be used to log into the ssh and transfer the files and get mac address:

please find the bits I need automated below

login="user@192.168.1.99" 
ssh_args="-o StrictHostKeyChecking=no"  

#Get the mac address 
mac=$(echo "ip -o link show dev eth0  | sed 's/.*link\/ether \([0-9:a-f]*\).*/\1/g'" | ssh $ssh_args $login)

if [[ $mac == "" ]]; then 
      exit
fi

 echo "CPE mac address == $mac"

scp $ssh_args -r system.cfg $login:/tmp/  

scp $ssh_args cp ../XM* $login:/tmp/fw.bin

You should be able to use the same SSH Key for each device - Can you explain further why you feel that SSH Key won't work for your situation, as this is the preferred solution to this sort of problem.

Thing is its not the same device everytime. the script configures routers devices automatically, updating their firmware etc...

I want this script to be applied for large amount of different devices thus I cant use SSH keys