Make endpoint methods as an alternative choice

Author: ArtyomVancyan

src/fastapi_oauth2/core.py

@@ -1,5 +1,5 @@
-import os
 import json
+import os
 import random
 import re
 import string
@@ -34,9 +34,8 @@ def absolute_uri(self, path=None) -> str:
         return path
 
     def get_setting(self, name) -> Any:
-        """ settings from environment """
         value = os.getenv(name)
-        if value == None:
+        if value is None:
             raise KeyError
         return value
 
@@ -69,8 +68,8 @@ def __init__(self, client: OAuth2Client) -> None:
         self.provider = client.backend.name
         self.redirect_uri = client.redirect_uri
         self.backend = client.backend(OAuth2Strategy())
-        self._authorization_endpoint = self.backend.authorization_url() if hasattr(self.backend, 'authorization_url') else self.backend.AUTHORIZATION_URL
-        self._token_endpoint = self.backend.access_token_url() if hasattr(self.backend, 'access_token_url') else self.backend.ACCESS_TOKEN_URL
+        self._authorization_endpoint = client.backend.AUTHORIZATION_URL or self.backend.authorization_url()
+        self._token_endpoint = client.backend.ACCESS_TOKEN_URL or self.backend.access_token_url()
         self._oauth_client = WebApplicationClient(self.client_id)
 
     @property