feat: Add MemberService (#3)

Author: youjin09222

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

@@ -0,0 +1,36 @@
+package com.gdsc_teamb.servertoyproject.login;
+
+import com.gdsc_teamb.servertoyproject.jwt.TokenInfo;
+import com.gdsc_teamb.servertoyproject.jwt.JwtTokenProvider;
+import lombok.RequiredArgsConstructor;
+import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
+import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
+import org.springframework.security.core.Authentication;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+@Transactional(readOnly = true)
+@RequiredArgsConstructor
+public class MemberService {
+
+    private final MemberRepository memberRepository;
+    private final AuthenticationManagerBuilder authenticationManagerBuilder;
+    private final JwtTokenProvider jwtTokenProvider;
+
+    @Transactional
+    public TokenInfo login(String memberId, String password) {
+        // 1. Login ID/PW 를 기반으로 Authentication 객체 생성
+        // 이때 authentication 는 인증 여부를 확인하는 authenticated 값이 false
+        UsernamePasswordAuthenticationToken authenticationToken = new UsernamePasswordAuthenticationToken(memberId, password);
+
+        // 2. 실제 검증 (사용자 비밀번호 체크)이 이루어지는 부분
+        // authenticate 매서드가 실행될 때 CustomUserDetailsService 에서 만든 loadUserByUsername 메서드가 실행
+        Authentication authentication = authenticationManagerBuilder.getObject().authenticate(authenticationToken);
+
+        // 3. 인증 정보를 기반으로 JWT 토큰 생성
+        TokenInfo tokenInfo = jwtTokenProvider.generateToken(authentication);
+
+        return tokenInfo;
+    }
+}