add access expiration properties to token and implement should_refres…

…h_token on fs backend

O365/utils/token.py

@@ -44,6 +44,26 @@ def expiration_datetime(self):
             expires_on = expires_on + dt.timedelta(days=90)
         return expires_on
 
+    @property
+    def access_expiry(self):
+        """
+        Returns the token's access expiration datetime
+        :return datetime: The datetime the token's access expires
+        """
+        expires_at = self.get('expires_at')
+        if expires_at:
+            return dt.datetime.fromtimestamp(expires_at)
+        else:
+            return dt.datetime.now() - dt.timedelta(seconds=10)
+
+    @property
+    def is_access_expired(self):
+        """
+        Returns whether or not the token's access is expired.
+        :return bool: True if the token's access is expired, False otherwise
+        """
+        return dt.datetime.now() > self.access_expiry
+
 
 class BaseTokenBackend(ABC):
     """ A base token storage class """
@@ -146,6 +166,9 @@ def __init__(self, token_path=None, token_filename=None):
         else:
             token_filename = token_filename or 'o365_token.txt'
             self.token_path = token_path / token_filename
+
+        # is this backend waiting on the filesystem
+        self.fs_wait = False
 
     def __repr__(self):
         return str(self.token_path)
@@ -199,6 +222,8 @@ def check_token(self):
         """
         return self.token_path.exists()
 
+    def should_refresh_token(self):
+        return not self.fs_wait
 
 class FirestoreBackend(BaseTokenBackend):
     """ A Google Firestore database backend to store tokens """