Serve Flask from a non-root path

flask_subpath.py

class FlaskSubpath(Flask):

    def __init__(self, *args, application_root="/", **kwargs):
        super().__init__(*args, **kwargs)
        self.application_root = application_root

    def wsgi_app(self, environ, start_response):
        if environ["PATH_INFO"].startswith(self.application_root):
            environ["PATH_INFO"] = environ["PATH_INFO"][len(self.application_root):]
            environ["SCRIPT_NAME"] = self.application_root
        elif "HTTP_FORWARDED_REQUEST_URI" in environ and environ["HTTP_FORWARDED_REQUEST_URI"].startswith(self.application_root):
            environ["SCRIPT_NAME"] = self.application_root
        return super().wsgi_app(environ, start_response)