How to use the ms-rest-azure.loginWithAppServiceMSI function in ms-rest-azure

var http = require('http');
const KeyVault = require('azure-keyvault');
const msRestAzure = require('ms-rest-azure');


var server = http.createServer(function(request, response) {
    response.writeHead(200, {"Content-Type": "text/plain"});
});

// The ms-rest-azure library allows us to login with MSI by providing the resource name. In this case the resource is Key Vault.
// For public regions the resource name is Key Vault
msRestAzure.loginWithAppServiceMSI({resource: 'https://vault.azure.net'}).then( (credentials) => {
    const keyVaultClient = new KeyVault.KeyVaultClient(credentials);

    var vaultUri = "https://" + "" + ".vault.azure.net/";
    
    // We're setting the Secret value here and retrieving the secret value
    keyVaultClient.setSecret(vaultUri, 'my-secret', 'test-secret-value', {})
        .then( (kvSecretBundle, httpReq, httpResponse) => {
            console.log("Secret id: '" + kvSecretBundle.id + "'.");
            return keyVaultClient.getSecret(kvSecretBundle.id, {});
        })
        .then( (bundle) => {
            console.log("Successfully retrieved 'test-secret'");
            console.log(bundle);
        })
        .catch( (err) => {
            console.log(err);

* Licensed under the MIT License. See License.txt in the project root for
 * license information.
 */
'use strict';
var http = require('http');
const KeyVault = require('azure-keyvault');
const msRestAzure = require('ms-rest-azure');


var server = http.createServer(function(request, response) {
    response.writeHead(200, {"Content-Type": "text/plain"});
});

// The ms-rest-azure library allows us to login with MSI by providing the resource name. In this case the resource is Key Vault.
// For public regions the resource name is Key Vault
msRestAzure.loginWithAppServiceMSI({resource: 'https://vault.azure.net'}).then( (credentials) => {
    const keyVaultClient = new KeyVault.KeyVaultClient(credentials);

    var vaultUri = "https://" + "" + ".vault.azure.net/";
    
    // We're setting the Secret value here and retrieving the secret value
    keyVaultClient.setSecret(vaultUri, 'my-secret', 'test-secret-value', {})
        .then( (kvSecretBundle, httpReq, httpResponse) => {
            console.log("Secret id: '" + kvSecretBundle.id + "'.");
            return keyVaultClient.getSecret(kvSecretBundle.id, {});
        })
        .then( (bundle) => {
            console.log("Successfully retrieved 'test-secret'");
            console.log(bundle);
        })
        .catch( (err) => {
            console.log(err);

getMSICredentials () {
        return msRestAzure.loginWithAppServiceMSI({resource: 'https://management.azure.com'});
        // return msRestAzure.interactiveLogin({resource: 'https://management.azure.com'});
    }

storeChallengeInKeyVault(challenge, secretData, callback) {
        assert.strictEqual(typeof challenge, 'object');
        assert.strictEqual(typeof secretData, 'string');
        assert.strictEqual(typeof callback, 'function');

        //replace illegal chars for secret name in kv
        let secretName = challenge.token.replace(/([^a-z0-9-]+)/gi, '');

        msRestAzure.loginWithAppServiceMSI({resource: 'https://vault.azure.net'}).then(credentials => {
            const keyVaultClient = new KeyVault.KeyVaultClient(credentials);

            keyVaultClient.setSecret(this.keyVaultUri, secretName, secretData, {})
                .then(kvSecretBundle => {
                    this.logMsg("KeyVaultSecret id: '" + kvSecretBundle.id + "'.");
                    callback(null, challenge);
                })
                .catch(err => {
                    callback('error storing keyvault secret ' + err)
                });
        })
        .catch(err => {
            callback('error logging in via MSI ' + err)
        });
    }

module.exports = function (context, req) {
    if(context && context.bindingData && context.bindingData.code && process.env.KEYVAULT_NAME) {
        //replace illegal chars for secret name in kv
        let secretName = context.bindingData.code.replace(/([^a-z0-9-]+)/gi, '');

        context.log(`Checking for ACME challenge response at '${secretName}'...`);

        msRestAzure.loginWithAppServiceMSI({resource: 'https://vault.azure.net'}).then(credentials => {
            const keyVaultClient = new KeyVault.KeyVaultClient(credentials);
            const vaultUri = `https://${process.env.KEYVAULT_NAME}.vault.azure.net/`;
            
            keyVaultClient.getSecret(vaultUri, secretName, "").then(secretData => {
                context.log(`ACME challenge response file '${secretName}' read successfully.`);
                context.log(secretData.value);

                context.res = {
                    status: 200,
                    headers: { "Content-Type": "text/plain" },
                    body: secretData.value
                };

                context.done();
            }).catch(err => {
                context.log.error(err);