gistfile1.txt

app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType);

app.UseCookieAuthentication(new CookieAuthenticationOptions());
//use OpenId
app.UseOpenIdConnectAuthentication(
  new OpenIdConnectAuthenticationOptions
  {

      ClientId = ...,
      Authority = ...,
      PostLogoutRedirectUri = "/",
      Notifications = new OpenIdConnectAuthenticationNotifications
      {
          AuthenticationFailed = context =>
          {
              context.HandleResponse();
              context.Response.Redirect("/Error?message=" + context.Exception.Message);
              return Task.FromResult(0);
          },

          SecurityTokenValidated = context =>
          {
              WriteTokenExipreTime(context.AuthenticationTicket.Properties.ExpiresUtc);
              
              // Login with Sitecore here.
              // Also map claims
              
              return Task.FromResult(0);
          },
      },
  });