M codes for JWT token

Hi,

I've successfully wrote M codes for API connections on several occasions, but I now have a new authentication method, which I haven't dealt with previously.  It is JWT (Json Web Token) and I need to write M codes to get JWT token, then use the JWT received to request for Access Token.  

I'm trying to figure out how to do the first part, getting JWT.

The 3rd party vendor (www.SwipeClock.com) has provided a sample code in Javascript, but I cannot replicate this in Power Query (Power BI).

Below is Javascript sample the vendor provided on their API Documentation:

<script src=http://kjur.github.io/ijsrasign/jsrsaign-latest-all-min.js”></script>
<script type=”text/javascript”>
	let header = {alg: “HS256”, type: “JWT”};

	let token = {
		iss: 69481,
    		exp: 1556729729,
 		 product: "twpclient",
  siteinfo: {
  			  type: "id",
  site: 69481
  				}
			}

	Let jwt = KJUR.jws.JWS.sign(“HS256”, JSON.stringify(header), JSON.stringify(token), “xxxxxxxSecretCodexxxxx”);

</script>

And here's my attempt to write it in Power BI (note, exp is Epoch time):

let

 GetJson = Json.Document(Web.Contents("https://clock.payrollservers.us/AuthenticationService/oauth2/usertoken",

   [
     Headers = [#"alg"= "HS256", #"typ"="JWT"],
 
    Content = [

#"iss"= 69481,
#"exp"= Number.ToText(Duration.TotalSeconds(DateTime.FixedLocalNow()-#datetime(1970,1,1,0,0,0)) + 60*5),
#"product"= "twpclient",

#"siteInfo"= [#"type"="id",#"site"= 69481]

    ],
    
    Query=   Json.FromValue(Headers)  &"." & Json.FromValue(Content)  &","& "xxxxxSecretCodexxxxxxxxx"
    
    ]
 
  ))

in
GetJson

Any help would be much appreciated!