README.md

Spring JWT

15.1 Encryption and Decryption

# Encryption : when sending the data using the key and convert it into cipher 
# Decryption : 

- 1. Symmetric Key : Will have the same key to encrypt and decrypt , It is faster and large key size 
Algos : AES , DES

- 2.  Asymmetric Key: where you have the piblic and private :
when the data is encrypt using public key need the another private key to decrypt 

- so when therer is multi-user or client they encrypt the data using the public key shared b/w them 
- and decrypted by it's private key combination.

Algos : RSA, ECDSA

Digital Signature :

- To verify the right owner we use the Digital Signature ,
- We have to encrypt the msg using the own pvt key , and to decrypt we have to share the public key.

# But in this process there is no security any one can read the data using the public key sender 

# To prevent the sec issue we can use the double encryption 1st encryption using the pub key of the 
user and sencond key as digital signature 

Why JWT and What is JWT :

# Scenario
- When we need the pass which have the digital sign of the authority 
- if the web is dynamic we need auth. but when the server is stateless ,
    we need to use the session to verify user , like using the session_ID
- if we have horizontal scalling server and it hsve the same db,
    or the load balancer send the particular user to destin server

- But instead of doing above thing we can give the pass to client , a signed pass 
like JSON Web Token (JWT) 

JWT Project Setup and Security and DB Config

 @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception
    {   
       
        http.csrf(customizer -> customizer.disable())
             .authorizeHttpRequests(request -> request
                    
                    .requestMatchers("/register","/hello")
                    .permitAll()
                    .anyRequest().authenticated())
             //.httpBasic(Customizer.withDefaults())
            // .httpBasic(withDefaults())
             .sessionManagement(session -> session.sessionCreationPolicy(SessionCreationPolicy.STATELESS));
        
        return  http.build();

    }

Custom Login

- [Login Controller](src/main/java/com/jspring6/SpringJWTproject/controller/UserController.java)

 @PostMapping("/login")
    public String login(@RequestBody User user)
    {
        Authentication authentication = authenticationManager
                 .authenticate(new UsernamePasswordAuthenticationToken(user.getUsername(), user.getPassword()));
        
        if(authentication.isAuthenticated())
        {
            return "User Logged In";
        }
        else
        {
            return "Invalid Credentials";
        }
    }

Generating Token using the Secret Key

- Token Generation

 private Key getKey()
    {   
        byte[] keyBytes = Decoders.BASE64.decode(secretKey);
        return Keys.hmacShaKeyFor(keyBytes);  // ask for the secret key message as bytestream 
    }

Creating JWT Filter

• when request is send the spring sec verify the credential using the username passwrd authentication

• We can use own custom method to check the credential usinng the filter

• as tomcat is servlet container --> sevlet is responsible to accept the user http request

• Http request and Http Response

• We can add the filter b/w the servlet and Servlet container when using the http req or response

• In filter we can modify the request data

• there can be multiple filter

• There is already inbuilt filter in spring sec. like UsernamePassword Filter

• we can add one more filter b/w jwtFilter

• can add filter before or filter after

JwtFilter

Adding the filter in Filter Chain:

    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception
    {   
       
        http.csrf(customizer -> customizer.disable())
             .authorizeHttpRequests(request -> request
                    
                    .requestMatchers("/register","/login")
                    .permitAll()
                    .anyRequest().authenticated())
             //.httpBasic(Customizer.withDefaults())
            // .httpBasic(withDefaults())
             .sessionManagement(session -> session.sessionCreationPolicy(SessionCreationPolicy.STATELESS))
             .addFilterBefore(jwtFilter, UsernamePasswordAuthenticationFilter.class);

            // adding the Jwt filter 
        return  http.build();

Setting Auth Token in Security Context

• jwtFilter

• Implementing OncePerRequestFilter

Validating the JWT token

• JWT Fiter

• JWT Service