Fetching device code endpoint from discovery (#245)

* Extracting device_endpt from discovery

Author: abhidnya13

msal/application.py

@@ -235,6 +235,7 @@ def _build_client(self, client_credential, authority):
             "authorization_endpoint": authority.authorization_endpoint,
             "token_endpoint": authority.token_endpoint,
             "device_authorization_endpoint":
+                authority.device_authorization_endpoint or
                 urljoin(authority.token_endpoint, "devicecode"),
             }
         return Client(

msal/authority.py

@@ -92,6 +92,7 @@ def __init__(self, authority_url, http_client, validate_authority=True):
         logger.debug("openid_config = %s", openid_config)
         self.authorization_endpoint = openid_config['authorization_endpoint']
         self.token_endpoint = openid_config['token_endpoint']
+        self.device_authorization_endpoint = openid_config.get('device_authorization_endpoint')
         _, _, self.tenant = canonicalize(self.token_endpoint)  # Usually a GUID
         self.is_adfs = self.tenant.lower() == 'adfs'