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

Question

I'm using OWIN / OAuth with OpenId Connect authentication (Microsoft.Owin.Security.OpenIdConnect) in a C# ASP MVC web app. The SSO login with Microsoft account basically works, but from time to time I'm getting an error page on the browser that says Bad Request - Request Too Long.

I found out that this error is caused by too many cookies. Deleting cookies helps for some time, but after a while the problem comes back.

The cookies that cause the problem are set from OpenId framework, so there are dozens of cookies with names like OpenIdConnect.nonce.9oEtF53WxOi2uAw........

This is not SPA application, but some parts are refreshed periodically with ajax calls.

Answer 1

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).