feat: 기존 깃허브 핸들명 조회 API 추가

Author: kimsh1017

src/main/java/com/gdschongik/gdsc/domain/discord/dto/response/DiscordGithubHandleResponse.java

@@ -0,0 +1,20 @@
+package com.gdschongik.gdsc.domain.discord.dto.response;
+
+public record DiscordGithubHandleResponse(String previousGithubHandle, String currentGithubHandle) {
+
+    private static final int VISIBLE_LENGTH = 4;
+
+    public static DiscordGithubHandleResponse of(String previousGithubHandle, String currentGithubHandle) {
+        return new DiscordGithubHandleResponse(maskHandle(previousGithubHandle), currentGithubHandle);
+    }
+
+    /**
+     * 앞 4자까지 노출하고 나머지를 '*'로 마스킹합니다. 4자 이하인 경우 최소 1자를 마스킹합니다.
+     * 예: "johndoe" → "john***", "abc" → "ab*", "a" → "*"
+     */
+    private static String maskHandle(String handle) {
+        int visibleLength = Math.min(handle.length() - 1, VISIBLE_LENGTH);
+        int maskLength = handle.length() - visibleLength;
+        return handle.substring(0, visibleLength) + "*".repeat(maskLength);
+    }
+}

src/main/java/com/gdschongik/gdsc/domain/member/api/OnboardingMemberController.java

@@ -1,19 +1,25 @@
 package com.gdschongik.gdsc.domain.member.api;
 
+import static com.gdschongik.gdsc.global.common.constant.RegexConstant.*;
+
+import com.gdschongik.gdsc.domain.discord.dto.response.DiscordGithubHandleResponse;
 import com.gdschongik.gdsc.domain.member.application.OnboardingMemberService;
 import com.gdschongik.gdsc.domain.member.dto.request.MemberInfoRequest;
 import com.gdschongik.gdsc.domain.member.dto.response.MemberDashboardResponse;
 import com.gdschongik.gdsc.domain.member.dto.response.MemberInfoResponse;
 import com.gdschongik.gdsc.domain.member.dto.response.MemberUnivStatusResponse;
 import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.media.Schema;
 import io.swagger.v3.oas.annotations.tags.Tag;
 import jakarta.validation.Valid;
+import jakarta.validation.constraints.Pattern;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestParam;
 import org.springframework.web.bind.annotation.RestController;
 
 @Tag(name = "Member - Onboarding", description = "회원 온보딩 API입니다.")
@@ -51,4 +57,15 @@ public ResponseEntity<MemberInfoResponse> getMemberInfo() {
         MemberInfoResponse response = onboardingMemberService.getMemberInfo();
         return ResponseEntity.ok().body(response);
     }
+
+    @Operation(summary = "GitHub 핸들 조회하기", description = "학번으로 해당 사용자의 GitHub 핸들을 조회합니다.")
+    @GetMapping("/github-handle")
+    public ResponseEntity<DiscordGithubHandleResponse> getGithubHandle(
+            @RequestParam("studentId")
+                    @Pattern(regexp = STUDENT_ID, message = "학번은 " + STUDENT_ID + " 형식이어야 합니다.")
+                    @Schema(description = "학번", pattern = STUDENT_ID)
+                    String studentId) {
+        DiscordGithubHandleResponse response = onboardingMemberService.getGithubHandleByStudentId(studentId);
+        return ResponseEntity.ok(response);
+    }
 }

src/main/java/com/gdschongik/gdsc/domain/member/application/OnboardingMemberService.java

@@ -2,6 +2,7 @@
 
 import static com.gdschongik.gdsc.global.exception.ErrorCode.*;
 
+import com.gdschongik.gdsc.domain.discord.dto.response.DiscordGithubHandleResponse;
 import com.gdschongik.gdsc.domain.email.application.UnivEmailVerificationService;
 import com.gdschongik.gdsc.domain.email.domain.UnivEmailVerification;
 import com.gdschongik.gdsc.domain.email.domain.service.EmailVerificationStatusService;
@@ -18,6 +19,7 @@
 import com.gdschongik.gdsc.domain.recruitment.domain.RecruitmentRound;
 import com.gdschongik.gdsc.global.exception.CustomException;
 import com.gdschongik.gdsc.global.util.MemberUtil;
+import com.gdschongik.gdsc.infra.github.client.GithubClient;
 import java.util.Optional;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
@@ -36,6 +38,7 @@ public class OnboardingMemberService {
     private final UnivEmailVerificationService univEmailVerificationService;
     private final MemberRepository memberRepository;
     private final EmailVerificationStatusService emailVerificationStatusService;
+    private final GithubClient githubClient;
 
     public MemberUnivStatusResponse checkUnivVerificationStatus() {
         Member currentMember = memberUtil.getCurrentMember();
@@ -69,6 +72,18 @@ public MemberDashboardResponse getDashboard() {
                 member, univVerificationStatus, currentRecruitmentRound.orElse(null), myMembership.orElse(null));
     }
 
+    public DiscordGithubHandleResponse getGithubHandleByStudentId(String studentId) {
+        Member currentMember = memberUtil.getCurrentMember();
+        String currentGithubHandle = githubClient.getGithubHandle(currentMember.getOauthId());
+
+        String previousGithubHandle = memberRepository
+                .findByStudentId(studentId)
+                .map(member -> githubClient.getGithubHandle(member.getOauthId()))
+                .orElseThrow(() -> new CustomException(MEMBER_NOT_FOUND));
+
+        return DiscordGithubHandleResponse.of(previousGithubHandle, currentGithubHandle);
+    }
+
     @Transactional
     public void attemptAdvanceToAssociate(long memberId) {
         Member member = memberRepository.findById(memberId).orElseThrow(() -> new CustomException(MEMBER_NOT_FOUND));