OAuth between Containers fails

[phishfi]

Hey all!

 

I have been working on getting CodiMD, a real-time collaboration tool for creating documents in Markdown, up and running. I've had it running no problem in the past, but the default configuration for that allowed anyone with access to the server to create an account and add/edit documents. There's a way to allow CodiMD to login via OAuth2, so I set that up using Nextcloud. I followed the instructions from CodiMD's Configuration Guide and their Nextcloud setup guide, but it seems the containers are unable to communicate with each other for the token exchange. What happens is Codi directs me to the NC auth site, then I confirm/allow Codi access to my NC account, then it directs me back to CodiMD and gives me an Internal Server Error 500. I have no clue how to correct this, and I've asked the CodiMD developers for help. We were able to determine that this appears to be an issue with Docker communication between the containers, because I'm unable to curl the public-facing URLs for either service from the docker terminal. It could be that my Nginx Proxy Manager isn't allowing the exchange to occur, but I have no idea how to correct that either. 

Any help on this would be greatly appreciated.