Strip Authorization header whenever root URL changes

Previously the header was stripped only if the hostname changed, but in
an https -> http redirect that can leak the credentials on the wire
(#4716). Based on with RFC 7235 section 2.2, the header is now stripped
if the "canonical root URL" (scheme+authority) has changed.

requests/sessions.py

@@ -239,10 +239,10 @@ def rebuild_auth(self, prepared_request, response):
         if 'Authorization' in headers:
             # If we get redirected to a new host, we should strip out any
             # authentication headers.
-            original_parsed = urlparse(response.request.url)
-            redirect_parsed = urlparse(url)
+            original_root = urljoin(response.request.url, '/')
+            redirect_root = urljoin(url, '/')
 
-            if (original_parsed.hostname != redirect_parsed.hostname):
+            if (original_root != redirect_root):
                 del headers['Authorization']
 
         # .netrc might have more auth for us on our new host.

tests/test_requests.py

@@ -1577,6 +1577,16 @@ def test_auth_is_stripped_on_redirect_off_host(self, httpbin):
         assert r.history[0].request.headers['Authorization']
         assert not r.request.headers.get('Authorization', '')
 
+    def test_auth_is_stripped_on_scheme_redirect(self, httpbin, httpbin_secure, httpbin_ca_bundle):
+        r = requests.get(
+            httpbin_secure('redirect-to'),
+            params={'url': httpbin('get')},
+            auth=('user', 'pass'),
+            verify=httpbin_ca_bundle
+        )
+        assert r.history[0].request.headers['Authorization']
+        assert not r.request.headers.get('Authorization', '')
+
     def test_auth_is_retained_for_redirect_on_host(self, httpbin):
         r = requests.get(httpbin('redirect/1'), auth=('user', 'pass'))
         h1 = r.history[0].request.headers['Authorization']