Here's a refined and corrected version of the end-to-end Google OAuth2 login integration using Spring Boot and Spring Security, with clean code snippets and no loose ends. This will give you a full working foundation:

✅ 1. Google Cloud Console Setup

1. Go to Google Cloud Console.

2. Create a new project.

3. Enable OAuth 2.0 Client IDs in APIs & Services > Credentials.

4. Configure OAuth consent screen (choose External).

5. Add Authorized Redirect URI (must match exactly):

   <http://localhost:8080/login/oauth2/code/google>
   
   

6. Copy the generated Client ID and Client Secret.

⚙️ 2. Spring Boot Configuration (application.yml)

spring:
  security:
    oauth2:
      client:
        registration:
          google:
            client-id: YOUR_CLIENT_ID
            client-secret: YOUR_CLIENT_SECRET
            scope: profile, email
        provider:
          google:
            authorization-uri: <https://accounts.google.com/o/oauth2/v2/auth>
            token-uri: <https://oauth2.googleapis.com/token>
            user-info-uri: <https://www.googleapis.com/oauth2/v3/userinfo>
            user-name-attribute: sub

🛡️ 3. Spring Security Configuration (SecurityConfig.java)

@Configuration
@EnableWebSecurity
public class SecurityConfig {

    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http
            .csrf().disable()
            .authorizeHttpRequests(authorize -> authorize
                .requestMatchers("/", "/oauth2/**").permitAll()
                .anyRequest().authenticated()
            )
            .oauth2Login(oauth2 -> oauth2
                .successHandler(customSuccessHandler())
            );

        return http.build();
    }

    @Bean
    public AuthenticationSuccessHandler customSuccessHandler() {
        return new OAuth2SuccessHandler(); // Custom logic to generate JWT
    }
}

🧠 4. Custom Success Handler (OAuth2SuccessHandler.java)

public class OAuth2SuccessHandler implements AuthenticationSuccessHandler {

    @Override
    public void onAuthenticationSuccess(HttpServletRequest request,
                                        HttpServletResponse response,
                                        Authentication authentication) throws IOException {
        OAuth2AuthenticationToken authToken = (OAuth2AuthenticationToken) authentication;
        Map<String, Object> attributes = authToken.getPrincipal().getAttributes();

        String email = (String) attributes.get("email");
        String name = (String) attributes.get("name");

        // Lookup or register user in DB (pseudo)
        // User user = userService.processOAuthPostLogin(email, name);

        // Generate JWT
        String jwt = JwtUtil.generateToken(email); // your custom utility

        response.setContentType("application/json");
        response.getWriter().write("{\\\\"token\\\\": \\\\"" + jwt + "\\\\"}");
    }
}

🔁 5. Frontend Triggers Login

The frontend starts the login by redirecting user to: