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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def change_credentials(self, user=None, auth_token=None):
 """ Change login credentials. :param str user: Username used to connect to server. :param str auth_token: Authentication token used to connect to server. """

        self.r_session.set_credentials(user, auth_token)
        self.r_session.login()