How can I change the method of a laravel request from GET to POST?

Question

In the middleware for a Laravel 10 app I have CAS authentication. When I call cas()->checkAuthentication() there is a chance that the call will go to the campus authentication server and be returned back later. The issue is that when there is a large form being filled out the cas call will often decide to check then and lose all the form data the user filled out. They will return the user to the same page, but as GET with no data.

Every time I get a POST call I save off the post data into the session before checking authentication and I can merge the post data back into the request. My question is, how can I change the request to follow the POST path instead of the GET path from the middleware?