'Add headers that are necessary for every request
This method adds ``token`` to the request.'

def add_default_headers(self, headers):

    b64string = b(('%s:%s' % (self.user_id, self.key)))
    token = base64.b64encode(b64string)
    headers['Authorization'] = ('Basic    %s' % token)
    headers['Accept'] = 'application/json'
    headers['Content-Type'] = 'application/json'
    return headers
