Adjust device flow api interface and behavior

Author: rayluo

msal/application.py

@@ -265,20 +265,17 @@ def initiate_device_flow(self, scopes=None, **kwargs):
             scope=decorate_scope(scopes or [], self.client_id),
             **kwargs)
 
-    def acquire_token_by_device_flow(
-            self, flow, exit_condition=lambda: True, **kwargs):
-        """Obtain token by a device flow object, with optional polling effect.
+    def acquire_token_by_device_flow(self, flow, **kwargs):
+        """Obtain token by a device flow object, with customizable polling effect.
 
         Args:
             flow (dict):
-                An object previously generated by initiate_device_flow(...).
-            exit_condition (Callable):
-                This method implements a loop to provide polling effect.
-                The loop's exit condition is calculated by this callback.
-                The default callback makes the loop run only once, i.e. no polling.
+                A dict previously generated by initiate_device_flow(...).
+                You can exit the polling loop early, by changing the value of
+                its "expires_at" key to 0, at any time.
         """
         return self.client.obtain_token_by_device_flow(
-                flow, exit_condition=exit_condition,
+                flow,
                 data={"code": flow["device_code"]},  # 2018-10-4 Hack:
                     # during transition period,
                     # service seemingly need both device_code and code parameter.

tests/test_application.py

@@ -142,9 +142,8 @@ def test_device_flow(self):
 
         duration = 30
         logging.warn("We will wait up to %d seconds for you to sign in" % duration)
-        result = self.app.acquire_token_by_device_flow(
-            flow,
-            exit_condition=lambda end=time.time() + duration: time.time() > end)
+        flow["expires_at"] = time.time() + duration  # Shorten the time for quick test
+        result = self.app.acquire_token_by_device_flow(flow)
         self.assertLoosely(
                 result,
                 assertion=lambda: self.assertIn('access_token', result),