How to use the node-opcua-crypto.exploreCertificate function in node-opcua-crypto

OPCUAClient.prototype._getApplicationUri = function () {

    // get applicationURI from certificate
    const exploreCertificate = require("node-opcua-crypto").exploreCertificate;

    const certificate = this.getCertificate();
    let applicationUri;
    if (certificate) {
        const e = exploreCertificate(certificate);
        if (!e.tbsCertificate.extensions  || !e.tbsCertificate.extensions.subjectAltName) {
            console.log(chalk.red(" Warning: client certificate is invalid : subjectAltName is missing"));
            applicationUri = makeApplicationUrn(hostname, this.applicationName);
        } else {
            applicationUri = e.tbsCertificate.extensions.subjectAltName.uniformResourceIdentifier[0];
        }
    } else {
        applicationUri = makeApplicationUrn(hostname, this.applicationName);
    }
    return applicationUri;

};

function validate_applicationUri(applicationUri, clientCertificate) {

        // if session is insecure there is no need to check certificate information
        if (channel.securityMode === MessageSecurityMode.NONE) {
            return true; // assume correct
        }
        if (!clientCertificate || clientCertificate.length === 0) {
            return true;// can't check
        }
        const e = exploreCertificate(clientCertificate);
        const applicationUriFromCert = e.tbsCertificate.extensions.subjectAltName.uniformResourceIdentifier[0];
        return applicationUriFromCert === applicationUri;
    }

function getUserName(userIdentityToken: UserIdentityToken): string {
    if (userIdentityToken instanceof AnonymousIdentityToken) {
        return "anonymous";
    }
    if (userIdentityToken instanceof X509IdentityToken) {
        const certInfo: CertificateInternals = exploreCertificate(userIdentityToken.certificateData);
        const userName = certInfo.tbsCertificate.subject.commonName || "";
        if (typeof userName !== "string") {
            throw new Error("Invalid username");
        }
        return userName;
    }
    if (userIdentityToken instanceof UserNameIdentityToken) {
        if (userIdentityToken.policyId === "anonymous") {
            return "anonymous";
        }
        assert(userIdentityToken.hasOwnProperty("userName"));
        return userIdentityToken.userName!;
    }
    throw new Error("Invalid user identity token");
}