How to use the node-opcua-service-session.AnonymousIdentityToken function in node-opcua-service-session

// clientCertificate
            clientCertificate: {dataType: "ByteString", value: session.channel.clientCertificate},

            // clientCertificateThumbprint
            clientCertificateThumbprint: {dataType: "ByteString", value: thumbprint(session.channel.clientCertificate)}

        });
    }
    // ----------------------------------------------------------------------------------------------------------------

    assert(response.authenticationToken);
    channel.send_response("MSG", response, message);
};

const UserNameIdentityToken = session_service.UserNameIdentityToken;
const AnonymousIdentityToken = session_service.AnonymousIdentityToken;

const getCryptoFactory = require("node-opcua-secure-channel").getCryptoFactory;

function adjustSecurityPolicy(channel, userTokenPolicy_securityPolicyUri) {
    // check that userIdentityToken
    let securityPolicy = fromURI(userTokenPolicy_securityPolicyUri);

    // if the security policy is not specified we use the session security policy
    if (securityPolicy === SecurityPolicy.Invalid) {
        securityPolicy = fromURI(channel.clientSecurityHeader.securityPolicyUri);
        assert(securityPolicy);
    }
    return securityPolicy;
}

OPCUAServer.prototype.isValidUserNameIdentityToken = function (channel, session, userTokenPolicy, userIdentityToken) {

/**
 * @module opcua.client
 */


const util = require("util");
const _ = require("underscore");
const assert = require("node-opcua-assert").assert;
const crypto = require("crypto");
const async = require("async");
const chalk = require("chalk");

const StatusCodes = require("node-opcua-status-code").StatusCodes;

const session_service = require("node-opcua-service-session");
const AnonymousIdentityToken = session_service.AnonymousIdentityToken;
const CreateSessionRequest = session_service.CreateSessionRequest;
const CreateSessionResponse = session_service.CreateSessionResponse;
const ActivateSessionRequest = session_service.ActivateSessionRequest;
const ActivateSessionResponse = session_service.ActivateSessionResponse;
const CloseSessionRequest = session_service.CloseSessionRequest;

const endpoints_service = require("node-opcua-service-endpoints");
const ApplicationDescription = endpoints_service.ApplicationDescription;
const ApplicationType = endpoints_service.ApplicationType;
const EndpointDescription = endpoints_service.EndpointDescription;
const MessageSecurityMode = require("node-opcua-service-secure-channel").MessageSecurityMode;

const SecurityPolicy = require("node-opcua-secure-channel").SecurityPolicy;
const getCryptoFactory = require("node-opcua-secure-channel").getCryptoFactory;
const fromURI = require("node-opcua-secure-channel").fromURI;