!!! Overview
[{$pagename}] is a [cookie] and is one of the most common [Authentication Methods] used within [Web Authentication] to know whether an [entity] is logged in or not, and which account they are logged in with. 

Without such some [Authentication Method], the site would not know whether to send a page containing sensitive information, or require the user to [authenticate] themselves by logging in. 

The security of an [Authentication cookie] generally depends on the security of the issuing [website] and the user's [web browser|user-agent], and on whether the [cookie] data is [encrypted|Encryption]. '

Security vulnerabilities may allow a [{$pagename}]'s data to be read by a hacker, used to gain access to user data, or used to gain access (with the user's [credentials]) to the website to which the [{$pagename}] belongs (see cross-site scripting and cross-site request forgery for examples).[1]

There is considerable movement away from [{$pagename}] to the use of [JSON Web Tokens] for [Authentication].

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]