Setting last logged-in timestamp on User table

Every time someone logs in using the default auth/login endpoint I want to update a field on their User record with the current timestamp.

So at the end of the function stack, after the Auth Token has been issued, I have an Add or Update record:
[Screen Shot 2022-10-11 at 4.58.49 pm.png]
The problem is that I get an access denied error – I assume because it's not an authenticated endpoint and the User table requires authentication.

How can I get around this? Do I need a separate table to store all login sessions or is there a simpler way?