asp.net 动态更改 Request.Header

public class Dev_Sim: IHttpModule
{
    public void Init(HttpApplication app)
    {
        app.BeginRequest += delegate { app.Context.Request.Headers.Add("UserName", "XYZZY"); };
    }

    public void Dispose(){}
}

void changeHeader(HttpApplication app)
        {
            var headers = app.Context.Request.Headers;
            Type hdr = headers.GetType();
            PropertyInfo ro = hdr.GetProperty("IsReadOnly",
                BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.IgnoreCase | BindingFlags.FlattenHierarchy);
            // Remove the ReadOnly property
            ro.SetValue(headers, false, null);
            // Invoke the protected InvalidateCachedArrays method 
            hdr.InvokeMember("InvalidateCachedArrays",
                BindingFlags.InvokeMethod | BindingFlags.NonPublic | BindingFlags.Instance,
                null, headers, null);
            // Now invoke the protected "BaseAdd" method of the base class to add the
            // headers you need. The header content needs to be an ArrayList or the
            // the web application will choke on it.
            hdr.InvokeMember("BaseRemove",
                BindingFlags.InvokeMethod | BindingFlags.NonPublic | BindingFlags.Instance,
                null, headers,
                new object[] { "User-Agent" });
            hdr.InvokeMember("BaseAdd",
                BindingFlags.InvokeMethod | BindingFlags.NonPublic | BindingFlags.Instance,
                null, headers,
                new object[] { "User-Agent", new ArrayList { "CustomHeaderContent" } });
            // repeat BaseAdd invocation for any other headers to be added
            // Then set the collection back to ReadOnly
            ro.SetValue(headers, true, null);
        }