How to use the jsrsasign.KJUR function in jsrsasign

exports.verify = function (token, pubhex, acceptable) {
  // verify JWT
  var options = merge(acceptable || {}, { alg: [ALGO] });
  var pubKey = new rs.KJUR.crypto.ECDSA({ curve: CURVE });
  pubKey.setPublicKeyHex(pubhex);
  pubKey.isPrivate = false;
  pubKey.isPublic = true;

  return rs.jws.JWS.verifyJWT(token, pubKey, options);
};

if (!key && retry && kid) {
            let error = 'expected key not found in property jwks. '
                            + 'This property is most likely loaded with the '
                            + 'discovery document. '
                            + 'Expected key id (kid): ' + kid;

            console.error(error);
            return Promise.reject(error);
        }

        let keyObj = rs.KEYUTIL.getKey(key);
        let validationOptions = {
            alg: this.allowedAlgorithms,
            gracePeriod: this.gracePeriodInSec
        };
        let isValid = rs.KJUR.jws.JWS.verifyJWT(params.idToken, keyObj, validationOptions);

        if (isValid) {
            return Promise.resolve();
        }
        else {
            return Promise.reject('Signature not valid');
        }
    }

function parseJwt(jwt) {
    return jsrsasign.KJUR.jws.JWS.parse(jwt)
}

runHexToPem: function(input, args) {
        return r.KJUR.asn1.ASN1Util.getPEMStringFromHex(input.replace(/\s/g, ""), args[0]);
    },

calcHash(valueToHash: string, algorithm: string): Promise {
    let hashAlg = new rs.KJUR.crypto.MessageDigest({ alg: algorithm });
    let result = hashAlg.digestString(valueToHash);
    let byteArrayAsString = this.toByteArrayAsString(result);
    return Promise.resolve(byteArrayAsString);
  }

runHexToObjectIdentifier: function(input, args) {
        return r.KJUR.asn1.ASN1Util.oidHexToInt(input.replace(/\s/g, ""));
    },

function validateJWT(pem, payload, exp) {
        var isValid = false;
        if (exp) {
            debug("JWT Expiry enabled");
            acceptField.verifyAt = rs.KJUR.jws.IntDate.getNow();
            try {
                isValid = rs.jws.JWS.verifyJWT(payload, pem, acceptField);
            } catch(e) {
                logger.consoleLog('log', {component: CONSOLE_LOG_TAG_COMP}, e.message );
            }
        } else {
            debug("JWT Expiry disabled");
            try {
                isValid = rs.jws.JWS.verify(payload, pem, acceptAlg);
            } catch(e) {
                logger.consoleLog('log', {component: CONSOLE_LOG_TAG_COMP}, e.message );
            }
        }
        return isValid;
    }

var server = http.createServer(function(request, response) {

     var privateKey = apigee.getVariable(request, "private.privateKey");
     var tstamp = rs.KJUR.jws.IntDate.get('now');
     
     //check for custom claims
     var customClaims = JSON.parse(apigee.getVariable(request, "claims")) || null;
     if (customClaims) {
         token = customClaims;
     }

     token.api_product_list = apigee.getVariable(request, "apiProductList");
     token.audience = "microgateway";
     token.jti = apigee.getVariable(request, "jti");
     token.iss = apigee.getVariable(request, "iss");
     token.access_token = apigee.getVariable(request, "apigee.access_token");
     token.client_id = apigee.getVariable(request, "apigee.client_id");
     token.nbf = tstamp;
     token.iat = tstamp;

_updateCertData() {
		//get x509 cert data
		try {
			const x509Path = this.beameStoreServices.getAbsoluteFileName(Config.CertFileNames.X509);

			const rs   = require('jsrsasign');
			const X509 = rs.X509;
			const fs   = require('fs');
			let pemStr = (fs.readFileSync(x509Path)).toString();
			let x      = new rs.X509();
			x.readCertPEM(pemStr);


			let hex          = X509.pemToHex(pemStr);
			let fingerprints = {
				    'sha1':   rs.KJUR.crypto.Util.hashHex(hex, 'sha1'),
				    'sha256': rs.KJUR.crypto.Util.hashHex(hex, 'sha256')
			    },
			    ai           = X509.getExtAIAInfo(hex),
			    alt          = X509.getExtSubjectAltName(hex),
			    keyUsageStr  = X509.getExtKeyUsageString(hex),
			    alg          = x.getSignatureAlgorithmField(),
			    subjectStr   = x.getSubjectString();

			let subject = {
				"commonName":   "",
				"country":      "",
				"locality":     "",
				"state":        "",
				"organization": ""
			};