title: Xero authentication - cannot pass custom URL parameter to backend
body: <p>I have a react application and node express backend API. I need to authenticate users for Xero. I'm using Xero node sdk (xero-node).</p>
  <p>However I want to identify the user from the backend when Xero callback url is called.</p>
  <p>I want to pass param1 as a custom parameter .</p>
  <p>My approach</p>
  <p>generating consent url and append a custom parameter.</p>
  <pre><code> const xero = new XeroClient({
      clientId: `..`,
      clientSecret: `..`,
      redirectUris: ['/callback'],
      scopes: 'openid email profile '.split(&quot; &quot;),
    });
    
    return xero.buildConsentUrl()+`&amp;param1=test`;
  </code></pre>
  <p>And I want to catch param1 in call back request.</p>
  <p>In express callback function</p>
  <pre><code>  console.log('url ',req.url); 
  </code></pre>
  <p>Unfortunately param1 doesn't exists on callback request.
  I thought about using state parameter, however it's preserved for OpenID related stuff. So is there any way to pass something to Xero auth url.</p>