Send a verify code via SMS to authenticate him/her

Scenario: in some countries (anyone said Italy?! :D ) public administration (PA) are still a bit sceptic to let users register without a stronger verify of their identity. Most of them trust SMS auhentication, because to get a mobile number you need to provide your Passport or Identity Card.

How does it work:

1) User "John Doe" register choosing a username, password, email ecc... and provide his mobile number too. Then he clicks on "Register" button.

2) "John Doe" is still on validation state.

3) AuthPuppy generates a random number from 10.000 to 99.999 (five numbers) and send an SMS to him with the generated code.

4) John comes back to authorization portal (AuthPuppy) and enter: username, password and confirmation number he got via SMS.

5) If the number is correct, AuthPuppy set him to "Validated".

What AuthPuppy should provide: AuthPuppy should provide the generic 99% of the code to implement this plugin. I mean the plugin itself, the possibility to modify registration form, verify the confirmation number ecc.....

What administrator using this plugin should provide: since there are many services available to send SMS (usually it's just few PHP lines of code), there should be a customizable section in the plugin:

function send_sms(from, to, message) { ..... }

the administrator should customize this function using the code provided by the SMS service he uses.