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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 password_credentials(self, username, password, **kwargs):
 """ Retrieve access token by 'password credentials' grant. https://tools.ietf.org/html/rfc6749#section-4.3 :param str username: The user name to obtain an access token for :param str password: The user's password :rtype: dict :return: Access token response """

        return self._token_request(grant_type='password',
                                   username=username, password=password,
                                   **kwargs)