Understand the session, cookie and token at one time, and the interview questions are all finalized

01、 What are they respectively ？

session：

session In the middle ⽂ The translation is “ conversation ”, When ⽤ User opens a web Should be ⽤ when , And web Server production ⽣⼀ Time session. The server makes ⽤session hold ⽤ The information of the user is temporarily saved on the server ,⽤ Leave ⽹ Post station session Will be destroyed . such ⽤ User information storage ⽅ The formula is relative to cookie It's safer , But session Yes ⼀ A flaw ： If web The server Load balancing is done , So ⼀ An operation request arrived at another ⼀ When it comes to servers session Will lose .

cookie：

cookie It is the data stored in the local terminal .cookie By the server ⽣ become , Send it to the browser , Browser handle cookie With kv Save the form to a ⽬ Recorded ⽂ Ben ⽂ In piece , Next ⼀ This request is the same as ⼀⽹ When you stand, you will cookie Send to the server . because cookie It's on the client side , So the browser adds ⼊ 了 ⼀ Some restrictions ensure that cookie Will not be maliciously used to ⽤, Same as Will not take up too much disk space , So for each domain cookie The quantity is limited .

cookie The composition of is ： name (key)、 value (value)、 Effective domain (domain)、 route ( Path to domain ,⼀ Set as global :“”)、 Failure time 、 Safety signs ( After designation ,cookie Only in making ⽤SSL Send to server when connected (https)).

token：

token It means “ token ”, yes ⽤ Household ⾝ Validation of copies ⽅ type , The simplest token form :uid(⽤ Huwei ⼀ Of ⾝ Copy identification )、time( Timestamp of current time )、sign( Signature , from token Before ⼏ position + Salt is hashed into ⼀ Fixed length ⼗ Hex string , It can prevent ⽌ Malicious third ⽅ Splicing token Request server ). You can also put constant parameters into the token, Avoid checking the library many times .

02、 What's the relationship between them ？

cookie,session It can be token A way to store .

cookie For data stored locally , When requested, the data will be submitted to the server for verification .

session For memory data stored on the server , As long as the session is not interrupted , Then the data remains valid .

toke Generally speaking, it belongs to token ,cookie,session It is a way of data storage and use , Tokens can be stored in cookie,session, But actually through url Parameters or form parameters can achieve the same effect . But the cost is high for development and maintenance , Once the backend requests to modify parameters , Such use is a headache for modification .

03、 Their essential differences ？

session The way to use is the client cookie Li Cun id, Server side session Save user data , When the client accesses the server , according to id Find user data .

and token The use of is stored in the client id（ That is to say token）、 User information 、 Ciphertext , There is nothing on the server , The server has only one piece of encryption code , It is used to judge whether the current encrypted ciphertext is consistent with the ciphertext passed by the client , If it's not consistent , That is, the user data of the client has been tampered , If the same , It means that the user data of the client is normal and correct .

technological process ：

session, Register login -> The server will user Deposit in session-> take sessioni In the browser cookie-> Visit again according to cookie Inside sessionid find session Inside user.

token, Register login -> The server generates a based on user information and key token-> take token+user Back to the browser -> When you visit again token+user+ Ciphertext data , The background will be used again user And key generation token, And passed on token Compare , Consistent is correct .

session、cookie、token These concepts often appear in interviews , Because through this concept, you can basically know whether you have any understanding and practical application of network request or permission management .

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