Check out number 19 on this list:

21 very useful htaccess tips & tricks. htaccess tips tricks | ViralPatel.net

...and the Cookie Manipulation and Tests with mod_rewrite

I hope that helps

Thanks, but I'm still way confused about how to set the cookie expiration. And make the cookie accessible by third party websites...

If this was the code...
Header set Set-Cookie "example-cookie=true"

What would I need to add to that code to make it expire Today's date + 365 days, and accessible by third party websites?

Thanks

As far as I know, you can't specifically set a cookie to be accessed by third party websites. The third party website needs to set their own cookies. You can let them to do that if you include something from the third party website in the content of your website, such as a banner.

Source: HTTP cookie - Wikipedia, the free encyclopedia

The syntax is:

Set-Cookie <name>=<value>[; <name>=<value>]...[; expires=<date>][;domain=<domain_name>][; path=<some_path>][; secure]

Example:

Header set Set-Cookie "example-cookie=true;expires=Sat, 01-Jan-2011 00:00:00 GMT;domain=mydomain.com;path=/;"

Not sure how to do the +365 days, perhaps there is some .htaccess guru here who knows?

If you find out, please post the answer here

You can use verbose time periods for expiry date instead of the explicit date: 1 month, 3 days, 2 hours, 1 year, etc.