Adding auth code flow support for public client (#149)

* Adding auth code flow support for public client

adal/authentication_context.py

@@ -179,7 +179,7 @@ def token_func(self):
 
     def acquire_token_with_authorization_code(self, authorization_code, 
                                               redirect_uri, resource, 
-                                              client_id, client_secret):
+                                              client_id, client_secret=None):
         '''Gets a token for a given resource via auhtorization code for a
         server app.
         
@@ -190,8 +190,9 @@ def acquire_token_with_authorization_code(self, authorization_code,
         :param str resource: A URI that identifies the resource for which the
             token is valid.
         :param str client_id: The OAuth client id of the calling application.
-        :param str client_secret: The OAuth client secret of the calling
-            application.
+        :param str client_secret: (only for confidential clients)The OAuth
+            client secret of the calling application. This parameter if not set,
+            defaults to None
         :returns: dict with several keys, include "accessToken" and
             "refreshToken".
         '''

adal/token_request.py

@@ -327,12 +327,13 @@ def get_token_with_authorization_code(self, authorization_code, client_secret):
             self._log.exception('Attempt to look for token in cache resulted in Error')
         oauth_parameters = self._create_oauth_parameters(OAUTH2_GRANT_TYPE.AUTHORIZATION_CODE)
         oauth_parameters[OAUTH2_PARAMETERS.CODE] = authorization_code
-        oauth_parameters[OAUTH2_PARAMETERS.CLIENT_SECRET] = client_secret
-
+        if client_secret is not None:
+            oauth_parameters[OAUTH2_PARAMETERS.CLIENT_SECRET] = client_secret
         token = self._oauth_get_token(oauth_parameters)
         self._cache_driver.add(token)
         return token
 
+
     def _get_token_with_refresh_token(self, refresh_token, resource, client_secret):
 
         self._log.info("Getting a new token from a refresh token")