Gets the access token for the app given the code

            Parameters:
                - code - the response code

def get_access_token(self, code):
        """ Gets the access token for the app given the code

            Parameters:
                - code - the response code
        """

        payload = {'redirect_uri': self.redirect_uri,
                   'code': code,
                   'grant_type': 'authorization_code'}

        headers = self._make_authorization_headers()

        response = requests.post(self.OAUTH_TOKEN_URL, data=payload,
            headers=headers, verify=LOGIN_VERIFY_SSL_CERT)
        if response.status_code is not 200:
            raise MercedesMeAuthError(response.reason)
        token_info = response.json()
        token_info = self._add_custom_values_to_token_info(token_info)
        self._save_token_info(token_info)
        return token_info