GHSA-MG3V-6M49-JHP3 WebOb's location header normalization during redirect leads to open redirect

Impact When WebOb normalizes the HTTP Location header to include the request hostname, it does so by parsing the URL that the user is to be redirected to with Python's urlparse, and joining it to the base URL. urlparse however treats a // at the start of a string as a URI without a scheme, and th...