I want to implement role based authentication in my app.
After researching for a while I found a simple solution - to pass role to signIn function

signIn('email', { email, role: 'user' });

Then I can unpack it from req's body

import NextAuth from 'next-auth'
export default async function auth(req, res) {
  return NextAuth(req, res, {
    // providers, adapters, etc.
    callbacks: {
      signIn: async ({ user }) => {
        const { body: { role } } = req;

        if (role) {
          user.role = role;
        }
        return true;
      },
      session: async ({ user, session }) => {
        session.user = {...session.user, ...user };
        return session
      }
    }
  }
});

Or so I thought. Magic link sign in flow has two steps: sending email and confirming it.

The role I provide to signIn function is only available during the first step and saving user to users collection only happens after user confirms email, so when user confirms email there's no role.

I tried storing role in cookies

if (role) res.setHeader('Set-Cookie', 'user-role=' + role + ';Max-Age=600');

But cookies get overriden after I confirm email and the role is lost.
I don't want to create additional collections and/or records in my database.

How can I preserve role inside signIn callback without storing it in a separate database collection? Maybe there's some other solution you can think of?