Authentication flow in Spring Boot

Introduction

Authentication flow helps check who a user is before letting them use an app. It keeps the app safe by making sure only real users get access.

When you want users to log in to your website or app.

When you need to protect certain pages or data from strangers.

When you want to remember users so they don’t have to log in every time.

When you want to check user identity before allowing actions like buying or editing.

When you want to log out users to keep their accounts safe.

Syntax

Spring Boot

public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .antMatchers("/public/**").permitAll()
                .anyRequest().authenticated()
            .and()
            .formLogin()
                .loginPage("/login")
                .permitAll()
            .and()
            .logout()
                .permitAll();
    }
}

This is a basic Spring Security setup for authentication flow.

It defines which URLs need login and which don’t.

Examples

Allow anyone to visit /home and /about without login, but require login for all other pages.

Spring Boot

http.authorizeRequests()
    .antMatchers("/home", "/about").permitAll()
    .anyRequest().authenticated();

Use a custom login page and send users to /dashboard after successful login.

Spring Boot

http.formLogin()
    .loginPage("/custom-login")
    .defaultSuccessUrl("/dashboard", true);

Set a custom logout URL and page shown after logout.

Spring Boot

http.logout()
    .logoutUrl("/signout")
    .logoutSuccessUrl("/goodbye");

Sample Program

This Spring Boot app sets up a simple authentication flow. Public URLs under /public are open to all. Other URLs require login. It uses a form login page at /login and allows logout.

Spring Boot

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.web.SecurityFilterChain;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    @EnableWebSecurity
    public static class SecurityConfig {

        @Bean
        public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
            http
                .authorizeHttpRequests(auth -> auth
                    .requestMatchers("/public/**").permitAll()
                    .anyRequest().authenticated()
                )
                .formLogin(form -> form
                    .loginPage("/login")
                    .permitAll()
                )
                .logout(logout -> logout
                    .permitAll()
                );
            return http.build();
        }
    }
}

Important Notes

Spring Security uses filters to check authentication on each request.

Always protect sensitive URLs by requiring authentication.

Customize login and logout pages for better user experience.

Summary

Authentication flow checks user identity before access.

Spring Security configures which pages need login.

Use form login and logout to manage user sessions.

Practice

1. What is the main purpose of the authentication flow in a Spring Boot application?

easy

A. To send emails to users after login

B. To style the user interface of the login page

C. To store user data in the database

D. To verify the identity of a user before granting access

Solution

1. Step 1: Understand authentication flow purpose

   Authentication flow is about checking who the user is before allowing access.

2. Step 2: Identify correct purpose in options

   Only To verify the identity of a user before granting access describes verifying user identity, which matches authentication.

3. Final Answer:

   To verify the identity of a user before granting access -> Option D

4. Quick Check:

   Authentication = Verify user identity [OK]

Hint: Authentication means checking who the user is [OK]

Common Mistakes:

• Confusing authentication with styling or data storage
• Thinking authentication sends emails
• Mixing authentication with authorization

2. Which of the following is the correct way to configure URL access rules in Spring Security?

easy

A. http.authorizeHttpRequests().requestMatchers("/admin/**").authenticated()

B. http.authorizeRequests().antMatchers("/private/**").denyAll()

C. http.authorizeRequests().anyRequest().allow()

D. http.authorizeRequests().requestMatchers("/public/**").permitAll()

Solution

1. Step 1: Identify correct method for URL rules in Spring Security

   Spring Security 6+ uses http.authorizeHttpRequests() with requestMatchers() for URL patterns.

2. Step 2: Check which option uses correct syntax and meaning

   http.authorizeHttpRequests().requestMatchers("/admin/**").authenticated() uses authorizeHttpRequests() and requestMatchers() with authenticated(), which is correct.

3. Final Answer:

   http.authorizeHttpRequests().requestMatchers("/admin/**").authenticated() -> Option A

4. Quick Check:

   Use authorizeHttpRequests() + requestMatchers() [OK]

Hint: Use authorizeHttpRequests() with requestMatchers() in Spring Security 6+ [OK]

Common Mistakes:

• Using deprecated authorizeRequests() in new Spring versions
• Using denyAll() incorrectly for access control
• Using anyRequest().allow() which is invalid

3. Given this Spring Security configuration snippet, what happens when a user accesses /dashboard without logging in?

http
  .authorizeHttpRequests(auth -> auth
    .requestMatchers("/public/**").permitAll()
    .anyRequest().authenticated()
  )
  .formLogin();

medium

A. The user can access /dashboard without login

B. The user is redirected to the login page

C. The user gets a 403 Forbidden error

D. The user sees a blank page

Solution

1. Step 1: Analyze URL access rules

   /public/** URLs are open, but any other request requires authentication.

2. Step 2: Check behavior for unauthenticated access to /dashboard

   Since /dashboard is not under /public, it requires login. formLogin() triggers redirect to login page.

3. Final Answer:

   The user is redirected to the login page -> Option B

4. Quick Check:

   Unauthenticated access redirects to login [OK]

Hint: AnyRequest().authenticated() means login required [OK]

Common Mistakes:

• Thinking permitAll() applies to all URLs
• Expecting 403 error instead of redirect
• Assuming access without login

4. Identify the error in this Spring Security configuration snippet:

http
  .authorizeHttpRequests(auth -> auth
    .requestMatchers("/admin/**").permitAll()
    .anyRequest().authenticated()
  )
  .formLogin();

medium

A. formLogin() is missing a login page URL

B. anyRequest().authenticated() should come before requestMatchers()

C. permitAll() on /admin/** allows unrestricted access to admin pages

D. requestMatchers() should be replaced with antMatchers()

Solution

1. Step 1: Review access rules for /admin/**

   permitAll() means anyone can access /admin/** without login, which is usually a security risk.

2. Step 2: Check order and methods

   Order is correct; anyRequest().authenticated() applies after permitAll(). formLogin() without URL uses default login page, which is valid.

3. Final Answer:

   permitAll() on /admin/** allows unrestricted access to admin pages -> Option C

4. Quick Check:

   permitAll() means open access [OK]

Hint: permitAll() means no login needed, risky on admin URLs [OK]

Common Mistakes:

• Thinking order of matchers is wrong here
• Assuming formLogin() needs explicit URL
• Confusing requestMatchers() with antMatchers()

5. You want to create a custom authentication flow that checks a user's email and password against a database and then grants access. Which Spring Boot component should you implement to handle this logic?

hard

A. UserDetailsService to load user data and PasswordEncoder to check password

B. AuthenticationEntryPoint to redirect users after login

C. CorsConfiguration to allow cross-origin requests

D. HttpFirewall to block unauthorized IP addresses

Solution

1. Step 1: Identify component for loading user info

   UserDetailsService is designed to load user details like email and password from a database.

2. Step 2: Identify component for password checking

   PasswordEncoder is used to verify the password matches the stored hash securely.

3. Step 3: Confirm other options are unrelated

   AuthenticationEntryPoint handles unauthorized access, not authentication logic. CorsConfiguration and HttpFirewall serve different purposes.

4. Final Answer:

   UserDetailsService to load user data and PasswordEncoder to check password -> Option A

5. Quick Check:

   Custom auth uses UserDetailsService + PasswordEncoder [OK]

Hint: UserDetailsService loads users; PasswordEncoder checks passwords [OK]

Common Mistakes:

• Confusing AuthenticationEntryPoint with authentication logic
• Using CorsConfiguration for authentication
• Thinking HttpFirewall handles login checks