'Add database user.
:param permissions: A ``(readFrom, writeTo)`` tuple'

def add_database_user(self, new_username, new_password, permissions=None):

    url = 'db/{0}/users'.format(self._database)
    data = {'name': new_username, 'password': new_password}
    if permissions:
        try:
            (data['readFrom'], data['writeTo']) = permissions
        except (ValueError, TypeError):
            raise TypeError("'permissions'    must    be    (readFrom,    writeTo)    tuple")
    self.request(url=url, method='POST', data=data, expected_response_code=200)
    return True
