How to implement SMS authentication on the site?

Question

Computer networks

Hello,
Please tell me how to implement SMS authentication. The following is of interest:
1) how is it generally arranged (in general terms), is some service used, or can I do this with the help of some software on the server?
2) is no longer interested in technical details, but purely to understand how it works.
3) in addition to authentication, it is also necessary to send messages depending on the actions of the visitor. For example, I made an order to the store, the status changed, I received an SMS.
Thank you very much for your replies, look forward to them!

Answer 1

If you are talking about all kinds of activation codes, then
1) The user enters the phone and presses send
2) You generate a code for it and write it to your database for the entered phone
3) Then using the services of any "SMS aggregator" or "SMS gate" - google on these say, thousands of them. Through the rest api of the service, send the number where to send and what to send, forgetting to pay for the services of the gate service.
4) The user receives a code from the aggregator, he enters, you compare it with what is in the database.