重构共享密钥生成逻辑，新增CryptUtils类以提供加密工具

core/src/main/java/com/xujiayao/discord_mc_chat/utils/CryptUtils.java

@@ -0,0 +1,54 @@
+package com.xujiayao.discord_mc_chat.utils;
+
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+import java.security.SecureRandom;
+
+/**
+ * Cryptographic utilities.
+ *
+ * @author Xujiayao
+ */
+public class CryptUtils {
+
+	private static final SecureRandom RANDOM = new SecureRandom();
+	private static final char[] ALPHANUMERIC = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789".toCharArray();
+
+	/**
+	 * Calculates the SHA-256 hash of a string.
+	 *
+	 * @param input The input string.
+	 * @return The hex string of the hash.
+	 */
+	public static String sha256(String input) {
+		try {
+			MessageDigest digest = MessageDigest.getInstance("SHA-256");
+			byte[] hash = digest.digest(input.getBytes(StandardCharsets.UTF_8));
+			StringBuilder hexString = new StringBuilder();
+			for (byte b : hash) {
+				String hex = Integer.toHexString(0xff & b);
+				if (hex.length() == 1) {
+					hexString.append('0');
+				}
+				hexString.append(hex);
+			}
+			return hexString.toString();
+		} catch (Exception e) {
+			throw new RuntimeException("SHA-256 algorithm not found", e);
+		}
+	}
+
+	/**
+	 * Generates a random alphanumeric string.
+	 *
+	 * @param length The length of the string.
+	 * @return The random string.
+	 */
+	public static String generateRandomString(int length) {
+		StringBuilder sb = new StringBuilder(length);
+		for (int i = 0; i < length; i++) {
+			sb.append(ALPHANUMERIC[RANDOM.nextInt(ALPHANUMERIC.length)]);
+		}
+		return sb.toString();
+	}
+}

core/src/main/java/com/xujiayao/discord_mc_chat/utils/config/ConfigManager.java

@@ -1,6 +1,7 @@
 package com.xujiayao.discord_mc_chat.utils.config;
 
 import com.fasterxml.jackson.databind.JsonNode;
+import com.xujiayao.discord_mc_chat.utils.CryptUtils;
 import com.xujiayao.discord_mc_chat.utils.StringUtils;
 import com.xujiayao.discord_mc_chat.utils.YamlUtils;
 import com.xujiayao.discord_mc_chat.utils.i18n.I18nManager;
@@ -11,8 +12,6 @@ import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
-import java.security.SecureRandom;
-import java.util.Base64;
 import java.util.function.Function;
 
 import static com.xujiayao.discord_mc_chat.Constants.LOGGER;
@@ -62,7 +61,7 @@ public class ConfigManager {
 
 					// If in standalone mode, generate a secure random shared secret
 					if ("standalone".equals(expectedMode)) {
-						String randomSecret = generateRandomSecret();
+						String randomSecret = CryptUtils.generateRandomString(32);
 						template = template.replace("shared_secret: \"to_be_auto_replaced\"", StringUtils.format("shared_secret: \"{}\"", randomSecret));
 					}
 
@@ -108,18 +107,6 @@ public class ConfigManager {
 		}
 	}
 
-	/**
-	 * Generates a cryptographically strong random string for the shared secret.
-	 *
-	 * @return A random 32-character string.
-	 */
-	private static String generateRandomSecret() {
-		SecureRandom random = new SecureRandom();
-		byte[] bytes = new byte[24]; // 24 bytes becomes 32 chars in Base64
-		random.nextBytes(bytes);
-		return Base64.getUrlEncoder().withoutPadding().encodeToString(bytes);
-	}
-
 	/**
 	 * Gets a specific configuration value as a JsonNode.
 	 *