Authentication flow in Spring Boot - Mini Project: Build & Apply

Authentication flow

📖 Scenario: You are building a simple Spring Boot application that needs to check user login credentials.This is like a door lock that only opens when the right key (username and password) is used.

🎯 Goal: Create a basic authentication flow in Spring Boot that checks a fixed username and password.When the user sends their username and password, the app will verify them and respond accordingly.

📋 What You'll Learn

Create a controller class named AuthController.

Add a POST endpoint /login that accepts username and password.

Use a fixed username user123 and password pass123 for validation.

Return a success message if credentials match, otherwise return an error message.

💡 Why This Matters

🌍 Real World

Authentication is a key part of almost every web application. This simple flow is like the front door check to allow users in.

💼 Career

Understanding how to build authentication endpoints is essential for backend developers working with Spring Boot or any web framework.

1

DATA SETUP: Create the AuthController class with fixed credentials

Create a class called AuthController annotated with @RestController. Inside it, define two private final String variables: correctUsername set to "user123" and correctPassword set to "pass123".

Spring Boot

@RestController
public class AuthController {
    // Your code here
}

Need a hint?

Use @RestController to make the class a REST controller.

Define two private final String variables for username and password.

2

CONFIGURATION: Add a POST mapping for /login with request body

Inside AuthController, add a method login annotated with @PostMapping("/login"). The method should accept a parameter of type LoginRequest annotated with @RequestBody. Create the LoginRequest class with two public String fields: username and password.

Spring Boot

@RestController
public class AuthController {
    private final String correctUsername = "user123";
    private final String correctPassword = "pass123";

    // Your code here
}

// Create LoginRequest class below
// Your code here

Need a hint?

Use @PostMapping("/login") to create the login endpoint.

Create a simple class LoginRequest with public fields for username and password.

3

CORE LOGIC: Implement credential checking inside login method

In the login method, check if request.username equals correctUsername and request.password equals correctPassword. If both match, return the string "Login successful". Otherwise, return "Invalid username or password".

Spring Boot

@RestController
public class AuthController {
    private final String correctUsername = "user123";
    private final String correctPassword = "pass123";

    @PostMapping("/login")
    public String login(@RequestBody LoginRequest request) {
        // Add credential check here
        // Your code here
    }
}

class LoginRequest {
    public String username;
    public String password;
}

Need a hint?

Use String.equals() to compare strings in Java.

Return the success message if both username and password match.

4

COMPLETION: Add class-level annotations and imports for Spring Boot

Add the necessary import statements for @RestController, @PostMapping, and @RequestBody from org.springframework.web.bind.annotation. Ensure the AuthController class is public and all code is properly structured.

Spring Boot

import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;

// Your code here

@RestController
public class AuthController {
    private final String correctUsername = "user123";
    private final String correctPassword = "pass123";

    @PostMapping("/login")
    public String login(@RequestBody LoginRequest request) {
        if (correctUsername.equals(request.username) && correctPassword.equals(request.password)) {
            return "Login successful";
        } else {
            return "Invalid username or password";
        }
    }
}

class LoginRequest {
    public String username;
    public String password;
}

Need a hint?

Import the Spring annotations to make the controller work.

Make sure the class is public.