title: IDX21323: RequireNonce is '[PII is hidden]'. OpenIdConnectProtocolValidationContext.Nonce was null, ValidatedIdToken.Payload.Nonce was not null
body: <p>I have an ASSP.NET MVC web application <code>MyWebApp</code> which doesn't allow anonymous access to any page. There is an <code>IdentityServer4</code> configured and once the user tries to open <code>MyWebApp</code>, he gets redirected to IdentityServer login page. (Hybrid Flow)
  The user does not login and stays on that IdentityServer login page for long enough so the <code>Nonce</code> cookie on <code>MyWebApp</code> expires (15min default lifetime).
  If he then proceeds with the login in IdentityServer (successful) and gets redirected back to <code>MyWebApp</code>, he gets the following error:</p>
  <blockquote>
  <p>Microsoft.IdentityModel.Protocols.OpenIdConnect.OpenIdConnectProtocolInvalidNonceException
  IDX21323: RequireNonce is '[PII is hidden]'.
  OpenIdConnectProtocolValidationContext.Nonce was null,
  OpenIdConnectProtocol.ValidatedIdToken.Payload.Nonce was not null. The
  nonce cannot be validated. If you don't need to check the nonce, set
  OpenIdConnectProtocolValidator.RequireNonce to 'false'. Note if a
  'nonce' is found it will be evaluated.</p>
  </blockquote>
  <p>But since the user was successfully authenticated in IdentityServer, when he tries to access <code>MyWebApp</code> again, he gets redirected to <code>IdentityServer</code> and back to <code>MyWebApp</code> without having to enter username/password again. Yet the initial error is annoying. Anyone ever had such issue when the 'login' flow has started and the user goes 'AFK' for long enough that the 'Nonce' cookie expires and he can't finish the final validation? What would be a good way to handle that scenario?</p>
  <p>Thanks in advance!</p>