fix: API 응답 실패 시, 이유 추가 (#65)

Author: KKangHHee

auth/src/main/java/com/jocketdan/auth/dto/CommonResponse.java

@@ -20,4 +20,8 @@ public static <T> CommonResponse<T> success(T data) {
     public static <T> CommonResponse<T> fail(String message) {
         return new CommonResponse<>(false, message, null);
     }
+
+    public static <T> CommonResponse<T> fail(String message, T reason) {
+        return new CommonResponse<>(false, message, reason);
+    }
 }

auth/src/main/java/com/jocketdan/auth/handlers/GlobalExceptionHandler.java

@@ -74,8 +74,10 @@ public ResponseEntity<CommonResponse<Void>> handleValidationException(MethodArgu
 
     // 그 외 모든 예상치 못한 예외
     @ExceptionHandler(Exception.class)
-    public ResponseEntity<CommonResponse<Void>> handleGlobalException(Exception e) {
+    public ResponseEntity<CommonResponse<String>> handleGlobalException(Exception e) {
         log.error("서버 오류", e);
-        return new ResponseEntity<>(CommonResponse.fail("서버 내부 오류가 발생했습니다."), HttpStatus.INTERNAL_SERVER_ERROR);
+        String reason = String.format("[%s] %s", e.getClass().getSimpleName(), e.getMessage());
+
+        return new ResponseEntity<>(CommonResponse.fail("서버 내부 오류가 발생했습니다.", reason), HttpStatus.INTERNAL_SERVER_ERROR);
     }
 }