Initiates the SLO process.

        :param return_to: Optional argument. The target URL the user should be redirected to after logout.
        :type return_to: string

        :param name_id: The NameID that will be set in the LogoutRequest.
        :type name_id: string

        :param session_index: SessionIndex that identifies the session of the user.
        :type session_index: string

        :param nq: IDP Name Qualifier
        :type: string

        :param name_id_format: The NameID Format that will be set in the LogoutRequest.
        :type: string

        :returns: Redirection url

def logout(self, return_to=None, name_id=None, session_index=None, nq=None, name_id_format=None):
        """
        Initiates the SLO process.

        :param return_to: Optional argument. The target URL the user should be redirected to after logout.
        :type return_to: string

        :param name_id: The NameID that will be set in the LogoutRequest.
        :type name_id: string

        :param session_index: SessionIndex that identifies the session of the user.
        :type session_index: string

        :param nq: IDP Name Qualifier
        :type: string

        :param name_id_format: The NameID Format that will be set in the LogoutRequest.
        :type: string

        :returns: Redirection url
        """
        slo_url = self.get_slo_url()
        if slo_url is None:
            raise OneLogin_Saml2_Error(
                'The IdP does not support Single Log Out',
                OneLogin_Saml2_Error.SAML_SINGLE_LOGOUT_NOT_SUPPORTED
            )

        if name_id is None and self.__nameid is not None:
            name_id = self.__nameid
        if name_id_format is None and self.__nameid_format is not None:
            name_id_format = self.__nameid_format

        logout_request = OneLogin_Saml2_Logout_Request(
            self.__settings,
            name_id=name_id,
            session_index=session_index,
            nq=nq,
            name_id_format=name_id_format
        )
        self.__last_request = logout_request.get_xml()
        self.__last_request_id = logout_request.id
        saml_request = logout_request.get_request()

        parameters = {'SAMLRequest': logout_request.get_request()}
        if return_to is not None:
            parameters['RelayState'] = return_to
        else:
            parameters['RelayState'] = OneLogin_Saml2_Utils.get_self_url_no_query(self.__request_data)

        security = self.__settings.get_security_data()
        if security.get('logoutRequestSigned', False):
            parameters['SigAlg'] = security['signatureAlgorithm']
            parameters['Signature'] = self.build_request_signature(saml_request, parameters['RelayState'], security['signatureAlgorithm'])
        return self.redirect_to(slo_url, parameters)