I'm trying to implement a phone number based login and not sure if I should ask the users for full number, i.e country code + number or just the number.
What I have in mind so far:
- Attempt optimistic login using whatever number user gives.
- Most likely, it'll come back with a single user match.
- In case there is a collision, throw an error (and show some helpful clue to the user asking them to enter full number)
I guess this is a simplistic approach with minimum friction and complexity (as opposed to IP detection, geography based resolution etc.).