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, by checking
scheme, hostname and port.

requests/sessions.py

@@ -242,7 +242,9 @@ class SessionRedirectMixin(object):
             original_parsed = urlparse(response.request.url)
             redirect_parsed = urlparse(url)
 
-            if (original_parsed.hostname != redirect_parsed.hostname):
+            if (original_parsed.hostname != redirect_parsed.hostname
+                    or original_parsed.port != redirect_parsed.port
+                    or original_parsed.scheme != redirect_parsed.scheme):
                 del headers['Authorization']
 
         # .netrc might have more auth for us on our new host.

tests/test_requests.py

@@ -1581,7 +1581,17 @@ class TestRequests:
             auth=('user', 'pass'),
         )
         assert r.history[0].request.headers['Authorization']
-        assert not r.request.headers.get('Authorization', '')
+        assert 'Authorization' not in r.request.headers
+
+    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 'Authorization' not in r.request.headers
 
     def test_auth_is_retained_for_redirect_on_host(self, httpbin):
         r = requests.get(httpbin('redirect/1'), auth=('user', 'pass'))