make client_id a class variable

this way one could overwrite it in user code if so desired

globustransferhelper.py

@@ -27,11 +27,11 @@ class GlobusTransferHelper:
     # TODO: move generic routines (for globus client) into base class
     tclient = None
     TIMEOUT = 60
+    CLIENT_ID = 'c87acef9-2bac-4743-90e8-2ae9e999ff29'
     # TODO add globus magic strings as constants
     def __init__(self):
         # this ID uniquely identifies the script to Globus together with the
         # access token it lets the script act on the user's behalf
-        CLIENT_ID = 'c87acef9-2bac-4743-90e8-2ae9e999ff29'
         REDIRECT_URI = 'https://auth.globus.org/v2/web/auth-code'
         SCOPES = 'openid email profile ' \
                  'urn:globus:auth:scope:transfer.api.globus.org:all'
@@ -43,13 +43,13 @@ class GlobusTransferHelper:
             tokens = self.load_tokens_from_file(TOKEN_FILE)
         except:
             # if we still need to get tokens, start the Native App authentication process
-            tokens = self.do_native_app_authentication(CLIENT_ID, REDIRECT_URI, SCOPES)
+            tokens = self.do_native_app_authentication(self.CLIENT_ID, REDIRECT_URI, SCOPES)
         try:
             self.save_tokens_to_file(TOKEN_FILE, tokens)
         except:
             pass
         transfer_tokens = tokens['transfer.api.globus.org']
-        auth_client = globus_sdk.NativeAppAuthClient(client_id=CLIENT_ID)
+        auth_client = globus_sdk.NativeAppAuthClient(client_id=self.CLIENT_ID)
         def refresh_callback(token_response):
             self.update_tokens_file_on_refresh(TOKEN_FILE, token_response)
         authorizer = globus_sdk.RefreshTokenAuthorizer(