Hi,
Just to clarify, do you wish to get the Customer ID associated with your generated OAuth2 credentials?
If yes, then you may do so by using the
CustomerService.getCustomers() along with the OAuth2 credentials generated without specifying any clientCustomerId in the request header. After which, you may then retrieve the
Customer ID from the returned
Customer object.
Let me know if this is what you are looking for or if you need further assistance.
Regards,
Ivan
AdWords API Team