Programmatically log in user via Credentials Provider in middleware via next-auth v5

[VladBo]

Background

I am using next-auth v5 for authentication and my application supports two types of sessions: guest and authenticated. To manage that, I am using two separate credentials providers. For guest sessions I need to programmatically log in users directly in the middleware.

Current approach

1. Redirect to a separate guest route endpoint in the middleware.
2. Trigger signIn server action from next-auth in that guest route endpoint.

Problem

This approach introduces an unnecessary redirect which causes white screen blinking. Ideally, I want to log in the user directly in the middleware. However, server actions cannot be called directly in middleware.

Question

How can I programmatically log in a user directly in the middleware without a redirect, given the constraint that server actions cannot be used in middleware?