How to implement a hot spot in which the password is sent via SMS to the phone entered in the form when you first connect to Wi-Fi?

Question

WiFi

There is a bar, the owner wants to organize a guest network in such a way that visitors, when connected to Wi-Fi, are authorized as follows:
- A welcome page opens with the institution's logo and a request to log in by entering your phone number and name;
- In response, you receive an SMS with a current password.
Further, the number is stored in the database, and in case of certain events related to the theme of the institution, an SMS is sent about the current special offer to all previously registered users.
One friend suggested that it can be implemented on openwrt by "screwing" a certain module to it, which can be synchronized with some SMS mailing service.
I would like to hear your opinion on this matter and possible solutions.
Thanks in advance to everyone who responds!