Using form authentication with asp.net identity side by side

public class ChallengeResult : HttpUnauthorizedResult
{
    public ChallengeResult(string provider, string redirectUri)
        : this(provider, redirectUri, null)
    {
    }

    public ChallengeResult(string provider, string redirectUri, string userId)
    {
        LoginProvider = provider;
        RedirectUri = redirectUri;
        UserId = userId;
    }

    public string LoginProvider { get; set; }
    public string RedirectUri { get; set; }
    public string UserId { get; set; }

    public override void ExecuteResult(ControllerContext context)
    {
        // HERE
        // this line did the trick
        context.RequestContext.HttpContext.Response.SuppressFormsAuthenticationRedirect = true;


        var properties = new AuthenticationProperties() { RedirectUri = RedirectUri };
        if (UserId != null)
        {
            properties.Dictionary[XsrfKey] = UserId;
        }

        context.HttpContext.GetOwinContext().Authentication.Challenge(properties, LoginProvider);
    }
}