Detailed introduction to the example code of php session control

Overview

http The protocol is stateless, and for each request, the server cannot distinguish between users. PHP session control gives the user a key (an encrypted session string), which is also a proof of the user's identity. The server stores the box (database, memory database or Made using files), the box contains the user's various variable information.

Where is this key?
1, url query string
2, browser cookie

traditional php session uses

 One question, where is the key? Didn’t you see the operation of giving the user the key? 
This operation is done for us behind PHP. Since you visit page1.php and the program runs, session_start();, PHP will generate it based on some conditions at the moment (user IP, browser number, time, etc.) A PHPSESSID variable. After the http response is returned to the client, this PHPSESSID is already stored in your browser cookie. Every time you visit this domain name again, the PHPSESSID will be sent to the server. This PHPSESSID is the user key I am talking about here. 
One more question, the security of this PHPSESSID, is it easy to be stolen, is it easy to be forged, is it easy to be tampered with? 
Using HTTPS can prevent tampering. Do not use PHPSESSID, but generate a secret key for the user to prevent forgery. As for whether it is easy to be stolen, there is really no research on it. For example, if your computer is connected to the Internet and hackers invade your computer. 
Save the generated secret key in the browser cookie
设置cookiesetCookie('key','value',time()+3600);
删除cookiesetCookie('key','',time()-1);
Realize single sign-on: session sharing
Single sign-on: share a set of users between multiple subsystems Authentication system, logging in from one place gives access to all subsystems. 
Imagine this scenario: Assume that the php environments of servers A and B are the same. The user got his key on server A, and then he took the key to access server B. Does he know server B? 
Obviously not, the key generated by server A is not recognized by the server. 
Solution: Regardless of whether the user accesses A or B, the generated key is stored in C (the same database, or cache system). When the user accesses A or B again, both A and B will ask C: This Is the user's key correct? If it is correct, the user can use the box stored in A or B. 
$uid,'session'=>session_encrypt(session_id().time()));
//下一步将，$session_info 存到　C 中
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