'Delete a credential and write the multistore.
This must be called when the multistore is locked.
Args:
client_id: The client_id for the credential
user_agent: The user agent for the credential
scope: The scope(s) that this credential covers'

def _delete_credential(self, client_id, user_agent, scope):

    key = (client_id, user_agent, scope)
    try:
        del self._data[key]
    except KeyError:
        pass
    self._write()
