feat: get private key through bouncycastle

build.gradle

@@ -43,6 +43,8 @@ dependencies {
     // Google Firebase Admin
     implementation 'com.google.firebase:firebase-admin:9.2.0'
     testImplementation 'org.springframework.boot:spring-boot-starter-test'
+    implementation group: 'org.bouncycastle', name: 'bcpkix-jdk15to18', version: '1.78.1' // 최신 버전 확인 후 사용
+
 }
 
 tasks.named('test') {

src/main/java/co/orange/ddanzi/service/auth/OAuthService.java

@@ -18,6 +18,8 @@
 import jakarta.transaction.Transactional;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
+import org.bouncycastle.asn1.pkcs.PrivateKeyInfo;
+import org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter;
 import org.springframework.core.io.ClassPathResource;
 import org.springframework.http.*;
 import org.springframework.stereotype.Service;
@@ -28,9 +30,8 @@
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStreamReader;
-import java.security.KeyFactory;
 import java.security.PrivateKey;
-import java.security.spec.PKCS8EncodedKeySpec;
+import java.security.Security;
 import java.time.LocalDateTime;
 import java.time.ZoneId;
 import java.util.*;
@@ -180,13 +181,14 @@ private String generateClientSecret() {
     }
 
     private PrivateKey getPrivateKey() {
+        Security.addProvider(new  org.bouncycastle.jce.provider.BouncyCastleProvider());
+        JcaPEMKeyConverter converter = new JcaPEMKeyConverter().setProvider("BC");
+
         try {
             byte[] privateKeyBytes = Base64.getDecoder().decode(appleProperties.getPrivateKey());
 
-            PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(privateKeyBytes);
-            KeyFactory keyFactory = KeyFactory.getInstance("EC"); // Elliptic Curve 키 타입 (ES256에 맞게)
-
-            return keyFactory.generatePrivate(keySpec);
+            PrivateKeyInfo privateKeyInfo = PrivateKeyInfo.getInstance(privateKeyBytes);
+            return converter.getPrivateKey(privateKeyInfo);
         } catch (Exception e) {
             throw new RuntimeException("Error converting private key from String", e);
         }