gistfile1.txt

def attach_handler(app):
    from flask import redirect, url_for
    app.wsgi_app = CustomProxyFix(app.wsgi_app)
 
class CustomProxyFix(object):
    def __init__(self, app):
        self.app = app
    def __call__(self, environ, start_response):
        host = environ.get('HTTP_X_FHOST', '')
        if host:
            environ['HTTP_HOST'] = host
        return self.app(environ, start_response)

FLASK_APP_MUTATOR = lambda app: attach_handler(app)