Cloudflare effecting GET requests to nginx and my Node.js server?

This would suggest the problem lies with passport when it’s ran thru a proxy.

So passport or whatever session system is passed to passport doesn’t like being behind a proxy.

So the issue is your nodeJS code and it’s ability to set session cookies.

So passport is completing the login, but it cannot correctly set the session cookie to “stick” the login.

How to fix that, depends on what is handling sessions for you