CSRF failing only on Django admin app?

[Dominique Cyprès]

Has anyone seen this issue before? I can successfully use a POST form with CSRF validation on a simple hand-coded Django app, but when I attempt to login to the standard Django admin app on the same project it fails CSRF validation every time—but only if I'm accessing it remotely, that is, through my Nginx reverse proxy. More details about my configuration and the errors I'm seeing on Stack Overflow:
https://stackoverflow.com/questions/62225484/csrf-verification-always-fails-when-accessing-django-admin-page-through-nginx-pr