Flask redirecting to HTTP URLs under the Compose stack

[multimeric]

Describe the bug

Flask redirects the user to http://some_url which is not being listened to, instead of https://some_url.

To Reproduce

Steps to reproduce the behavior:

1. Run the compose stack
2. Create a user account
3. You will be directed to an HTTP URL

Expected behavior

You should be directed to an HTTPS URL

Additional context

Since we're using an nginx proxy in this stack, it seems likely that this is the cause of the problem: https://stackoverflow.com/a/45693122/2148718.