I am trying to generate AWS Cloudfront singed url using apex but every time get Access Denied.

public url is working fine. i.e. jueh890044563.cloudfront.net/test.pdf

But I need a singed url of cloudfront.

I have already done following things in AWS.

S3 bucket is private.
test.pdf is private.
Created cloudfront Distribution (domain name is : jueh890044563.cloudfront.net)

Apex code

String keyPairId = 'YTEHJLKFHHRKF';
Datetime now = DateTime.now();
Datetime expireson = now.addDays(2);
Long Lexpires = expireson.getTime()/1000;

String policyStatement = '{"Statement":[{"Resource":"jueh890044563.cloudfront.net/test.pdf","Condition":{"DateLessThan":{"AWS:EpochTime":'+Lexpires+'}}}]}';

policyStatement = EncodingUtil.base64Encode(Blob.valueOf(policyStatement));

String privateKey = 'dfgdfgtgdfgdfgdfsgdfgdfsgdfgdfgdfgsdf'+
'dfgdfgdfgdfgdfgdfgdfgdfgdfgfgdfgdfsdf'+
'dfdfgdfgdfgdfgdfgfdgdfg/i0AB1Jz20QlGy'+
'dsfgdfgdfgdfgdfgdfgdsfgdfgdfgffdfgdfg';

Blob mac = Crypto.generateMac('HmacSHA1', blob.valueof(policyStatement),blob.valueof(privateKey));
String signed = EncodingUtil.base64Encode(mac);

String downloadUrl = 'jueh890044563.cloudfront.net/test.pdf?Policy='+policyStatement+'&Signature='+signed+'&Key-Pair-Id='+keyPairId;

Is downloadUrl is singedUrl? When we run this url then return Access Denied.

Thanks in advance.

I've been working with developing a stand-alone app in lightning. In trying to adhere to the look and feel I'm following the html layed out in https://www.lightningdesignsystem.com/components/tabs. Sorry if this is a newb question how do I manipulate the class of the <a> being clicked to .slds-active and it's corresponding <div> to .slds-show , and then remove any other existing <a> with the .slds-active and change the <div> to .sld.slds-hide?  I've seen something similiar with javascript on a visualforce page but I wanted to follow the component design structure. Surely someone has done this as it seems pretty standard navigation. Currently my component has

<div class="slds-tabs--default">
 <ul class="slds-tabs--default__nav" role="tablist">
   <li class="slds-tabs--default__item slds-text-heading--label slds-active" title="Item One" role="presentation">
   <a class="slds-tabs--default__link" href="#void" role="tab" tabindex="0" aria-selected="true" aria-controls="tab-default-1" data-data="tab-default-1__item"  onclick="{!c.selectTab}" id="tab-default-1__item">New Checklists</a>
        </li>
  <li class="slds-tabs--default__item slds-text-heading--label" title="Item Two" role="presentation">
            <a class="slds-tabs--default__link" href="#void" role="tab" tabindex="-1" aria-selected="false" aria-controls="tab-default-2" data-data="tab-default-2__item" onclick="{!c.selectTab}" id="tab-default-2__item">Existing Checklist</a>
        </li>
      </ul>
      <div id="tab-default-1" class="slds-tabs--default__content slds-show" role="tabpanel" aria-labelledby="tab-default-1__item">
        <h2>Item One Content</h2>
      </div>
      <div id="tab-default-2" class="slds-tabs--default__content slds-hide" role="tabpanel" aria-labelledby="tab-default-2__item">
        <h2>Item Two Content</h2>
      </div>

    </div>

I have the onClick="{!c.selectTab}" which goes to my js controller. Below

selectTab : function(component, event, helper){
    	var activeTab;
        activeTab = event.target.getAttribute("id");
        //var result = component.find("tab-default-1__item");
        //alert(result);
  
    },

I see the event.target.getAttribute gives me the value of the onclick id. I can get the value and can then tell which tab was clicked, but then how do I 

1. Change the class value of that Id?
2. Change the class value of other id's?

I've been trying to use various javascript  functions like find but nothing seems to be working. Can someone point me to which functions I should be using to find id(DOMS) on a component and which functions can be used to set vairous attributes?  I didn't find anything in the lightning dev guide but will keep looking. Any help is appreciated.
 

I would like to use a visualforce template to attache details of a knowledge article.

I have tried using the Articles as PDF field that works for Text and HTML emails, but this does not wotk.

Is there any way to do this??

Thanks