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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 retrieve_api_token(self):
 """ Retrieve the access token from AVS. This function is memoized, so the value returned by the function will be remembered and returned by subsequent calls until the memo expires. This is because the access token lasts for one hour, then a new token needs to be requested. Decorators: helpers.expiring_memo Returns: str -- The access token for communicating with AVS """


        payload = self.oauth2_manager.get_access_token_params(
            refresh_token=self.refresh_token
        )
        response = requests.post(
            self.oauth2_manager.access_token_url, json=payload
        )
        response.raise_for_status()
        response_json = json.loads(response.text)
        return response_json['access_token']