Add Client.is_expired

Fixes #754

oauthlib/oauth2/rfc6749/clients/base.py

@@ -213,12 +213,16 @@ def add_token(self, uri, http_method='GET', body=None, headers=None,
         if not (self.access_token or self.token.get('access_token')):
             raise ValueError("Missing access token.")
 
-        if self._expires_at and self._expires_at < time.time():
+        if self.is_expired():
             raise TokenExpiredError()
 
         return case_insensitive_token_types[self.token_type.lower()](uri, http_method, body,
                                                                      headers, token_placement, **kwargs)
 
+    def is_expired(self):
+        """Returns true when the access token is expired."""
+        return self._expires_at and self._expires_at < time.time()
+
     def prepare_authorization_request(self, authorization_url, state=None,
                                       redirect_url=None, scope=None, **kwargs):
         """Prepare the authorization request.

tests/oauth2/rfc6749/clients/test_base.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 import datetime
 from unittest.mock import patch
+import time
 
 from oauthlib import common
 from oauthlib.oauth2 import Client, InsecureTransportError, TokenExpiredError
@@ -135,6 +136,17 @@ def test_add_bearer_token(self):
         self.assertRaises(ValueError, client.add_token, self.uri, body=self.body,
                 headers=self.headers)
 
+    def test_is_expired(self):
+        expired = 523549800
+        expired_token = {'expires_at': expired}
+        client = Client(self.client_id, token=expired_token, access_token=self.access_token, token_type="Bearer")
+        self.assertTrue(client.is_expired())
+
+        not_expired = time.time() + 60 * 10
+        token = {'expires_at': not_expired}
+        client = Client(self.client_id, token=token, access_token=self.access_token, token_type="Bearer")
+        self.assertFalse(client.is_expired())
+
     def test_add_mac_token(self):
         # Missing access token
         client = Client(self.client_id, token_type="MAC")