How to get browser certificate to digitally sign a payload using Chrome Extension

I am working on a chrome extension to get access to the list of certificates on my browser (Including the class 3 certificate I purchased).

This is the manifest.json

 {
"manifest_version": 2,
"name": "Coding Train Extension 2",
"version": "0.001",
"permissions": ["storage", "activeTab", "scripting"],
"content_scripts": [
    {
        "matches":["<all_urls>"],
        "js": ["content.js"]
    }
],
 "background":{
   "scripts": ["background.js"]
 },
 "browser_action":{
   "default_icon": "logo.png"

 }
} 

This is the background.js

 console.log("This is inside background...");
 chrome.browserAction.onClicked.addListener(collectAvailableCertificates);

 function collectAvailableCertificates() {
   // Return all certificates that this Extension can currently provide.
   // For example:
   return [{
     certificateChain: [new Uint8Array()],
     supportedAlgorithms: ['RSASSA_PKCS1_v1_5_SHA256']
    }];
   }

In this test, the content.js is not being used much. I have an icon of the extension on browser and on its click I am triggering the background.js.
I am trying to emulate the APIs provided in the Chrome API documentation https://developer.chrome.com/docs/extensions/reference/certificateProvider/

How to call the methods like collectAvailableCertificates(), handleSignatureRequest(request) as seen in the document is what I am pursuing. My aim is to use this purchased certificate to digitally sign an xml payload.