feat: kakaoService 구현

추후에 삭제 예정

related to: #11

src/main/java/com/_119/wepro/auth/service/KakaoService.java

@@ -0,0 +1,73 @@
+package com._119.wepro.auth.service;
+
+import com._119.wepro.auth.dto.request.AuthRequest.SignInRequest;
+import com._119.wepro.auth.dto.response.AuthResponse.SignInResponse;
+import com._119.wepro.global.enums.Provider;
+import com._119.wepro.auth.client.KakaoOauthClient;
+import com._119.wepro.auth.dto.response.KakaoTokenResponse;
+import lombok.RequiredArgsConstructor;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestTemplate;
+import org.springframework.web.util.UriComponentsBuilder;
+
+@Service
+@RequiredArgsConstructor
+public class KakaoService {
+
+  private final KakaoOauthClient kakaoOauthClient;
+
+  // 임시
+  private static final String LOGIN_URI = "http://localhost:8080/login";
+
+  @Value("${kakao.client-id}")
+  private String CLIENT_ID;
+
+  @Value("${kakao.redirect-uri}")
+  private String REDIRECT_URI;
+
+  @Value("${kakao.client-secret}")
+  private String CLIENT_SECRET;
+
+  @Value("${kakao.authorization-uri}")
+  private String KAKAO_AUTH_URL;
+
+  // 백엔드용
+  public String generateKakaoRedirectUrl() {
+    return UriComponentsBuilder.fromUriString(KAKAO_AUTH_URL)
+        .queryParam("client_id", CLIENT_ID)
+        .queryParam("redirect_uri", REDIRECT_URI)
+        .queryParam("response_type", "code")
+        .build()
+        .toUriString();
+  }
+
+  // 백엔드용
+  public SignInResponse handleKakaoCallback(String code) {
+    KakaoTokenResponse tokenResponse = kakaoOauthClient.kakaoAuth(CLIENT_ID, REDIRECT_URI, code,
+        CLIENT_SECRET);
+    String idToken = tokenResponse.getIdToken();
+    ResponseEntity<SignInResponse> response = callLoginApiWithIdToken(idToken);
+
+    return response.getBody();
+  }
+
+  // 백엔드용
+  private ResponseEntity<SignInResponse> callLoginApiWithIdToken(String idToken) {
+    RestTemplate restTemplate = new RestTemplate();
+    SignInRequest signInRequest = new SignInRequest(Provider.KAKAO, idToken);
+
+    HttpHeaders headers = new HttpHeaders();
+    headers.setContentType(MediaType.APPLICATION_JSON);
+    HttpEntity<SignInRequest> requestEntity = new HttpEntity<>(signInRequest, headers);
+
+    ResponseEntity<SignInResponse> response = restTemplate.postForEntity(LOGIN_URI, requestEntity,
+        SignInResponse.class);
+
+    return response;
+  }
+}