Enhance OnFunctionInvocationAsync Method in AnonymouseUserFilter Class

[brianrandell]

Issue Description

The OnFunctionInvocationAsync method in the AnonymouseUserFilter class needs to be enhanced with better detection logic, specifically in the following code:

if (context.Arguments.TryGetValue("userName", out var userName) && userName!.ToString() == "guest")
{
    context.Result = new FunctionResult(context.Function, "No discounts for anonymous users allowed");
    return;
}

Expected Behavior

Improve the detection logic to handle edge cases and provide better validation.

Additional Information

This enhancement is necessary to ensure robustness in handling anonymous users.