OAuth2 소셜 로그인

# application.properties
spring.security.oauth2.client.registration.google.client-id=${GOOGLE_CLIENT_ID}
spring.security.oauth2.client.registration.google.client-secret=${GOOGLE_CLIENT_SECRET}
spring.security.oauth2.client.registration.google.scope=profile,email

# SecurityConfig에 OAuth2 추가
http.oauth2Login(oauth2 -> oauth2
    .userInfoEndpoint(info -> info
        .userService(customOAuth2UserService))
    .successHandler(oAuth2SuccessHandler));

// CustomOAuth2UserService.java
@Service
@RequiredArgsConstructor
public class CustomOAuth2UserService extends DefaultOAuth2UserService {
    private final UserRepository userRepository;

    @Override
    public OAuth2User loadUser(OAuth2UserRequest request) throws OAuth2UserException {
        OAuth2User oAuth2User = super.loadUser(request);
        String registrationId = request.getClientRegistration().getRegistrationId();
        OAuth2UserInfo userInfo = OAuth2UserInfoFactory.getOAuth2UserInfo(
            registrationId, oAuth2User.getAttributes());

        User user = userRepository.findByEmail(userInfo.getEmail())
            .orElseGet(() -> userRepository.save(
                User.builder()
                    .email(userInfo.getEmail())
                    .name(userInfo.getName())
                    .provider(registrationId)
                    .build()));
        return new CustomOAuth2User(user, oAuth2User.getAttributes());
    }
}