Event to authorize access to IW forms

[cprmlao@hotmail.com]

Hi,

I have many forms in my project.
I have created a table to put the rights of each user. 
Some users only can access some forms.

What  would be the better event to check if a user is authorized to load and see the form?
I´d like to show a dialog message in that event if the user is not authorized.

I think is a a event in servercontroller. But, what? and How to send  a async message to browse saying the user is not authorized? Is possible to send a message from servercontroller and not from a form?

I will appreciate some others ideas about it

Regards , 
Luiz