How to cancel user creation?

[sachinraja]

In the profile callback, I am checking localStorage to see if username exists. Is there any way to cancel the creation of a new user without erroring if username does not exist?

[balazsorban44]

Please provide more information. Why would you save anything in localStorage about the user? Please note that this might be a security issue, as localStorage is easily readable by malicious actors.

Anyways, to stop a user being logged in, we provide the following API:

https://next-auth.js.org/configuration/callbacks#sign-in-callback

[sachinraja]

I am not saving anything sensitive about the user. Before each user signs up, I want them to create a unique username. My plan is to persist their requested username in localStorage and fetch that upon user creation.

[sachinraja]

Hey, thank you for letting me know. I plan on using a cookie (as localStorage cannot be accessed from an API anyway). I actually saw the signIn callback when I was researching earlier, but didn't think it was what I needed because it says you can use it to "control if a user is allowed to sign in." Perhaps it should be documented that it will actually cancel user creation if they do not already have an account?