How can I setup two factor auth (sms) via ssh connection

I am writing a bash script on ubuntu 16.04 and I want to setup **Two factor authentification via SMS on SSH connection** to the server. I saw that there is a way to do it with a google authentication system. But for that the client must download an app first. I want to send a SMS (simple text that contain a code) to a cell phone that the user will use plus his password to gain access to the server. Even if I can use a service or a non-free gateway via an api to send the SMS. Could you help me please?? Thanks you.