I want to Monitor users who subscribe to my RSS Feeds.

How can i use an authentication Process to block users from getting access.

the normal RSS feed is

• just a url
• to a specially formated file

To 'control' that access, you would need your users to 'login' before accessing it,
and that breaks the RSS subscription data flow; ie any Pop3 email client can 'subscribe' to an RSS feed.

To 'monitor' without control, place a fixed image in the feed, like the FAVICO.ico file reference. Now your server logs will contain an entry for each time it's served.

Instead of the FAVICO.ico, which is served to every browser that accesses ANY content on the server, create your own gif in some other location,

eg rss/rssaccessed.gif

and each 'hit' was from a RSS subscription.

Ah, clever.

Then, just look through the IP's of individuals who have accessed your .gif file and block the IP of who ever you don't want viewing your RSS feed?

hmmmmm; blocking IP addresses is unreliable and you can't be sure you've
a) got the right guy(s)
b) they didn't access it from elsewhere, say a hotspot.

Again: monitoring is different that access control

you might try a Public vs Private concept, where

• /Public/rss/* is accessible via a link anywhere on your site and could be emailed as you see fit
  
  
• /Private/rss/* has no links anywhere and the only access is when you tell someone how to find it

but don't delude yourself - - - if JoeDoe knows of /Private, 10 minutes later, hist friends will too.