Flask-OpenID issues with proxy server
It sounds like your proxy server isnt passing on the HOST header, using nginx you can use proxy_set_header Host $host; in your location directive.
You may also want to look at setting the X-Forwarded-For and X-Forwarded-Proto headers so you can read the actual client IP and protocol correctly. Werkzeug provides a fixer to help with this, and there's an example detailed in the Flask docs, request.remote_addr should then be what you expect.
Here's a more complete nginx location directive:
location / { proxy_pass http://localhost:8000/; proxy_set_header Host $host; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-Forwarded-Proto $scheme;}