One Time Registration Code

[e1412]

I am trying to create an authentication for a form.

Its like an application. If you don't enter a code provided by me, you can't access the form.
Please how do i do that ?

Challenges;
1. If code is not associated to a user ID, code should still remain valid.
2. Code should work only once
3. Two or more users entering code at same time (one must be invalid).

[penders]

...you can't access the form.

Presumably you mean the user will not be able to submit the form successfully? (They would need to "access the form" wouldn't they?)

I'm not sure which bit you are stuck on?

Assuming one code for one user, the basic principle could be something like:

1. You issue a unique code to a particular user (and tell the user somehow by email, sms, phone, etc.) The code is assigned to the user record in the database.

2. User enters code and submits form.

3. If code matches code in users record then success and remove code from database. Otherwise reject.