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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 authenticate(self, username, password):
 """Authenticates your user and returns an auth token. :param str username: Hummingbird username. :param str password: Hummingbird password. :returns: str -- The Auth Token :raises: ValueError -- If the Authentication is wrong """


        r = self._query_('/users/authenticate', 'POST',
                         params={'username': username,
                                 'password': password})
        if r.status_code == 201:
            return r.text.strip('"')
        else:
            raise ValueError('Authentication invalid.')