feat: Add CustomUserDetailsService (#3)

server-toy-project/src/main/java/com/gdsc_teamb/servertoyproject/login/CustomUserDetailsService.java

@@ -0,0 +1,34 @@
+package com.gdsc_teamb.servertoyproject.login;
+
+import com.gdsc_teamb.servertoyproject.domain.user.domain.UserEntity;
+import lombok.RequiredArgsConstructor;
+import org.springframework.security.core.userdetails.User;
+import org.springframework.security.core.userdetails.UserDetails;
+import org.springframework.security.core.userdetails.UserDetailsService;
+import org.springframework.security.core.userdetails.UsernameNotFoundException;
+import org.springframework.security.crypto.password.PasswordEncoder;
+import org.springframework.stereotype.Service;
+
+@Service
+@RequiredArgsConstructor
+public class CustomUserDetailsService implements UserDetailsService {
+
+    private final MemberRepository memberRepository;
+    private final PasswordEncoder passwordEncoder;
+
+    @Override
+    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
+        return memberRepository.findByMemberId(username)
+                .map(this::createUserDetails)
+                .orElseThrow(() -> new UsernameNotFoundException("해당하는 유저를 찾을 수 없습니다."));
+    }
+
+    // 해당하는 User 의 데이터가 존재한다면 UserDetails 객체로 만들어서 리턴
+    private UserDetails createUserDetails(Member member) {
+        return User.builder()
+                .username(member.getUsername())
+                .password(passwordEncoder.encode(member.getPassword()))
+                .roles(member.getRoles().toArray(new String[0]))
+                .build();
+    }
+}