Too many cookies OpenIdConnect.nonce cause error page "Bad Request - Request Too Long"

It turned out that the root cause was the Ajax call.

The problematic flow was

1) OAuth cookie got expired after some time

2) Expiration normally causes redirection the page to login.microsoft.com to refresh the cookie. In this step OAuth framework adds new nonce cookie to the response (every time)!

3) But Ajax doesn't handle redirections outside of the domain (cross-domain to login.microsoft.com). But the cookie was already appended to the page.

4) Next periodical Ajax call repeated the flow causing rapid increase of 'nonce' cookies.

Solution

I had to extend the "OWIN OpenId" framework setup code to handle Ajax calls differently - to prevent redirection and stop sending cookies.

public void ConfigureAuth(IAppBuilder app)
{
    app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType);
    app.UseCookieAuthentication(new CookieAuthenticationOptions());

    app.UseOpenIdConnectAuthentication(
        new OpenIdConnectAuthenticationOptions
        {
            ClientId = clientId,
            Authority = authority,
            Notifications = new OpenIdConnectAuthenticationNotifications
            {
                RedirectToIdentityProvider = ctx => 
                {
                    bool isAjaxRequest = (ctx.Request.Headers != null && ctx.Request.Headers["X-Requested-With"] == "XMLHttpRequest");

                    if (isAjaxRequest)
                    {
                        ctx.Response.Headers.Remove("Set-Cookie");
                        ctx.State = NotificationResultState.HandledResponse;
                    }

                    return Task.FromResult(0);
                }
            }
        });
}

The Ajax caller had to be adjusted too to detect 401 code and perform full page refresh (which caused a quick redirect to Microsoft authority).

For me the solution was to enforce the creation of an ASP.NET session.

Steps to reproduce:

• Delete ASP.NET_SessionId cookie and idsrv cookie on a protected page of your webapp
• Reload page
• Redirect to OIDC authentication store and authenticate
• Redirect back to webapp => validation of the authentication fails, because no asp.net session is available
• Endless redirects until 'Request too long...' error happens

Solution: Enforce session creation by adding

protected void Session_Start(object sender, EventArgs e)
{
}

to global.asax.cs.