APEX

Hi all,

I noticed that if i changed my page number in the URL, i could access a page in my application that requires a higher access level than my access level.
I was reading the apex book and found page sentry function.

My understanding is i can use this attribute to verify whether a user have a valid access to the page.
My question are:
1. Since I need to verify the username against the page id. Where do i get the page_id and username information from, to be pass in to my function?
2. Can anyone share an example of this function?
I look around the internet and the book. I couldn't find a simple example that i could easily understand the concept.


Thanks before.
-Joel