Nextcloud login works on local IP, getting "wrong username or password" after placing it behind reverse proxy

Hey folks,

I've been at this one all day and it's driving me nuts. I followed SpaceInvader's most recent nextcloud walkthrough to a T. I created the admin account in nextcloud when it was on my local IP, but once it's placed behind the reverse proxy I use the same exact login info and get "wrong username or password".

Is my nextclooud instance losing it's connection to the db behind the proxy or something? I'm not sure what other info I could provide to make this easier to troubleshoot but any help is certainly appreciated.

* This is a fresh install of both Mariadb and Nextcloud. * I have removed and reinstalled both continers twice with fresh installs (and removed all appdata files). * I am able to log in fine after removing the proxy again

Thanks in advance for any help.