Today I encountered a problem in Flask, that caused my links to be not found.

After googling and an hour of trial and error, I finally found a solution. Here it is.

Solution To HTTP Redirect Instead Of HTTPS

In the NGINX configuration file add this parameter proxy_set_header X-Forwarded-HTTPS on; under the location section

location @proxy_to_app {
            proxy_pass http://myweb.local:5000;         # <- let nginx pass traffic to the gunicorn server
            proxy_ssl_server_name on;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header   X-Forwarded-HTTPS    on;   # Fix logout url for redirects to http instead of https
        }

Now every time I click on the link, that was created by using URL_FOR Redirect syntax, I go straight to the correct HTTPS URL.

Failed Solution On StackOverflow

It took me an hour to go through all kinds of answers. Below are the ones, that didn't work for me.

External = True

using _external=True inside url_for

Preferred URL Scheme

app.config.update(dict(
  PREFERRED_URL_SCHEME = 'https'
))

Nginx Forwarded Proto Scheme

proxy_set_header   X-Forwarded-Proto    $scheme;

Enforce URL Scheme

def _force_https(app):
    def wrapper(environ, start_response):
        environ['wsgi.url_scheme'] = 'https'
        return app(environ, start_response)
    return wrapper

app = Flask(...)

app = _force_https(app)

Conclusion

If you want your links to use HTTPS instead of HTTP, just edit your NGINX configuration.