def _get_auth_header(self):
        ''' Constructs and returns an authentication header. '''
        realm = 'realm="{realm}"'.format(realm=self.realm)
        params = ['{k}="{v}"'.format(k=k, v=quote(str(v), safe=''))
                  for k, v in self.oauth_params.items()]
        return 'OAuth ' + ','.join([realm] + params)
Constructs and returns an authentication header.