Prepare request authorization header

function prepareRequest(resource: DashboardCardResource, variables: { [key: string] : string }, pat: string) {

  let url = SubtituteString(resource.absoluteUrl, variables);

  const httpOptions = new HttpHeaders({ 
    'Authorization': `Basic ${btoa(`"":${pat}`)}`, 
    'Accept': 'application/json' 
  });

  return { url, httpOptions };
}