Sustainsys Saml2 HandledResult = true still sets the cookie

On AcsCommandResultCreated, I want to set my custom cookie. However, I end up with two cookies: one created by the library and another that is mine, even though I set HandledResult = true. How can I have only my authentication cookie?

Here's my code:

options.SPOptions.ModulePath = samlRoutePrefix;
options.SignInScheme = "SamlTemp";

options.Notifications.AcsCommandResultCreated = (commandResult, _) =>
{
    var httpContext = httpContextAccessor.HttpContext;
    if (httpContext == null)
        throw new InvalidOperationException("HttpContext not available — ensure IHttpContextAccessor is registered.");

    var completeSamlLogin = httpContext.RequestServices.GetRequiredService<ICompleteSamlLogin>();
    var authenticationCookieContentMapper = httpContext.RequestServices.GetRequiredService<IAuthenticationCookieContentMapper>();

    var relayState = httpContext.Request.Form[SamlConstants.RelayStateKey].ToString();

    var claimsPrincipal = commandResult.Principal;

    var email = ExtractEmailFromClaims(claimsPrincipal);
    if (string.IsNullOrEmpty(email))
        throw new UnauthenticatedException("No email address found in SAML response.");

    var firstName = claimsPrincipal.FindFirst(ClaimTypes.GivenName)?.Value;
    var lastName = claimsPrincipal.FindFirst(ClaimTypes.Surname)?.Value;

    var input = new CompleteSamlLoginInput
    {
        RelayState = relayState,
        Email = email,
        FirstName = firstName,
        LastName = lastName
    };

    var loginOutput = completeSamlLogin.Execute(input).Result;
    var cookieContent = authenticationCookieContentMapper.Map(loginOutput);

    httpContext.CreateAuthenticationCookieAsync(cookieContent, true).GetAwaiter().GetResult();

    commandResult.Headers.Add(SCloudHeaderNames.AntiCsrfToken, cookieContent.AntiCsrfToken.ToString());

    commandResult.HandledResult = true;
};