local server bind address (#202)

This PR adds the bind_addr parameter to run_local_server. When using localhost inside of a container this is needed to allow the redirect server to bind to an address to which response will return. In a container this address is not the same as the host address of localhost.

- [x] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/google-auth-library-python-oauthlib/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
- [x] Ensure the tests and linter pass
- [x] Code coverage does not decrease (if any source code was changed)
- [x] Appropriate docs were updated (if necessary)

Fixes #201 🦕

Author: gilesknap

google_auth_oauthlib/flow.py

@@ -443,6 +443,7 @@ def run_console(
     def run_local_server(
         self,
         host="localhost",
+        bind_addr=None,
         port=8080,
         authorization_prompt_message=_DEFAULT_AUTH_PROMPT_MESSAGE,
         success_message=_DEFAULT_WEB_SUCCESS_MESSAGE,
@@ -463,6 +464,11 @@ def run_local_server(
         Args:
             host (str): The hostname for the local redirect server. This will
                 be served over http, not https.
+            bind_addr (str): Optionally provide an ip address for the redirect
+                server to listen on when it is not the same as host
+                (e.g. in a container). Default value is None,
+                which means that the redirect server will listen
+                on the ip address specified in the host parameter.
             port (int): The port for the local redirect server.
             authorization_prompt_message (str): The message to display to tell
                 the user to navigate to the authorization URL.
@@ -483,7 +489,7 @@ def run_local_server(
         # Fail fast if the address is occupied
         wsgiref.simple_server.WSGIServer.allow_reuse_address = False
         local_server = wsgiref.simple_server.make_server(
-            host, port, wsgi_app, handler_class=_WSGIRequestHandler
+            bind_addr or host, port, wsgi_app, handler_class=_WSGIRequestHandler
         )
 
         redirect_uri_format = (

tests/unit/test_flow.py

@@ -403,6 +403,24 @@ def assign_last_request_uri(host, port, wsgi_app, **kwargs):
 
         assert not webbrowser_mock.open.called
 
+    @mock.patch("google_auth_oauthlib.flow.webbrowser", autospec=True)
+    @mock.patch("wsgiref.simple_server.make_server", autospec=True)
+    def test_run_local_server_bind_addr(
+        self, make_server_mock, webbrowser_mock, instance, mock_fetch_token
+    ):
+        def assign_last_request_uri(host, port, wsgi_app, **kwargs):
+            wsgi_app.last_request_uri = self.REDIRECT_REQUEST_PATH
+            return mock.Mock()
+
+        make_server_mock.side_effect = assign_last_request_uri
+
+        my_ip = socket.gethostbyname(socket.gethostname())
+        instance.run_local_server(bind_addr=my_ip, host="localhost")
+
+        assert webbrowser_mock.open.called
+        name, args, kwargs = make_server_mock.mock_calls[0]
+        assert args[0] == my_ip
+
     @pytest.mark.webtest
     @mock.patch("google_auth_oauthlib.flow.webbrowser", autospec=True)
     def test_run_local_server_occupied_port(