feat: SecurityContextHolder 에서 email 리턴 메서드 구현

server/src/main/java/com/ticketing/server/global/security/SecurityUtil.java

@@ -0,0 +1,21 @@
+package com.ticketing.server.global.security;
+
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.context.SecurityContextHolder;
+
+public class SecurityUtil {
+
+	private SecurityUtil() {
+	}
+
+	public static String getCurrentUserEmail() {
+		final Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
+
+		if (authentication == null || authentication.getName() == null) {
+			throw new IllegalStateException("Security Context 에 인증 정보가 없습니다.");
+		}
+
+		return authentication.getName();
+	}
+
+}