Feature Request: Built-in Phone Number Recycling Support for Authentication

[leonaburime-ucla]

Problem
When phone numbers are recycled (old number assigned to new person), Supabase Auth prevents linking the recycled number to a new user account, showing the error:

AuthApiError: A user with this phone number has already been registered

This creates a poor user experience where legitimate users cannot verify their phone numbers simply because the number was previously owned by someone else.

Current Workaround
The current solution requires:

1. Creating an admin Edge Function to manually unlink phone numbers from previous users
2. Complex client-side logic to coordinate OTP sending and verification with phone unlinking
3. Additional security considerations to prevent abuse

Proposed Solution
Supabase could implement built-in phone number recycling support with one of these approaches:

Option 1: Automatic Unlinking After Successful OTP Verification

When a user requests OTP for a phone number already linked to another account
Allow OTP to be sent (perhaps with a flag indicating potential conflict)
After successful OTP verification, automatically unlink the phone from the previous account and link to the current user
This proves the new user has control of the phone number

Option 2: Configuration Option for Phone Number Uniqueness

Add a project setting to disable strict phone number uniqueness
Allow multiple users to have the same phone number temporarily
Provide hooks/triggers for custom conflict resolution

Option 3: Built-in Phone Number Recycling API

New auth methods like auth.requestPhoneRecycling() and auth.verifyPhoneRecycling()
Handle the unlinking logic internally after OTP verification

Use Cases
Users getting new phone numbers that were previously used
International users where phone number recycling is common
Business applications where phone verification is critical