Really simple DialogFlow V2 JS connection with jQuery

main.js

var projectID = "xxxx-xxxx";
// session-id can apparently be set to an arbitrary value, eg. "abcd1234-abcd-abcd-abcd-abcd12345678".
var sessionID = "xxxx-xxxx";
var serviceAccountEmail = "xxxx-xxxxx@xxxxxxxx.iam.gserviceaccount.com";
var serviceAccountPrivateKey = "-----BEGIN PRIVATE KEY-----\nXXXXXXX==\n-----END PRIVATE KEY-----\n";

var ClaimSet = /** @class */ (function () {
    function ClaimSet(scopes, issuerEmail) {
        this.scopes = scopes;
        this.issuerEmail = issuerEmail;
        this.audienceURL = "https://www.googleapis.com/oauth2/v4/token";
        this.duration = 60 * 60 * 1000;
    }
    ClaimSet.prototype.ToSpecClaimSet = function () {
        var issuedAtTime = this.issuedAtTime || Date.now();
        var expireAtTime = issuedAtTime + this.duration;
        return {
            scope: this.scopes.join(" "),
            iss: this.issuerEmail,
            sub: this.delegationEmail,
            aud: this.audienceURL,
            iat: Math.floor(issuedAtTime / 1000),
            exp: Math.floor(expireAtTime / 1000)
        };
    };
    return ClaimSet;
}());


function GetAssertion(claimSet, privateKey) {
    //TS: var header = { alg: "RS256", typ: "JWT" };

    // Header
    var oHeader = {alg: 'RS256', typ: 'JWT'};
    // Payload
    var oPayload = claimSet.ToSpecClaimSet();
    // Sign JWT, password=616161
    var sHeader = JSON.stringify(oHeader);
    var sPayload = JSON.stringify(oPayload);
    //TS: return KJUR.jws.JWS.sign(header.alg, header, claimSet.ToSpecClaimSet(), privateKey);
    return KJUR.jws.JWS.sign(oHeader.alg, sHeader, sPayload, privateKey);
}

// Get token:

var cs = new ClaimSet(["https://www.googleapis.com/auth/cloud-platform"], serviceAccountEmail);
var assertion = GetAssertion(cs, serviceAccountPrivateKey);
console.log(assertion);

$.when( $.post({
    url: "https://www.googleapis.com/oauth2/v4/token",
    headers: {
        "content-type": "application/json"
    },
    data: JSON.stringify({
        grant_type: "urn:ietf:params:oauth:grant-type:jwt-bearer",
        assertion: assertion
    })
}) ).then(function( data, textStatus, jqXHR ) {
  if (data == null) {
    // Whenever you want...
    return;
  }
  access_token = data.access_token;
  $.when( $.post({
      url: "https://dialogflow.googleapis.com/v2/projects/" + projectID + "/agent/sessions/" + sessionID +  ":detectIntent",
      headers: {
        "authorization": "Bearer " + access_token,
        "content-type": "application/json",
      },
      data: JSON.stringify({
        queryInput: {
          text: {
            "text": "hello",
            "language_code": "en-US"
          }
        },
        queryParams: {
          timeZone: "Europe/Madrid",
        }
      })
  }) ).then(function( data, textStatus, jqXHR ) {
    console.log( data ); 
    console.log( data.queryResult.fulfillmentText );
  });

});