private MongoCredential createCredentail(String group) {
		final Setting setting = this.setting;
		if(null == setting) {
			return null;
		}
		final String user = setting.getStr("user", group, setting.getStr("user"));
		final String pass = setting.getStr("pass", group, setting.getStr("pass"));
		final String database = setting.getStr("database", group, setting.getStr("database"));
		return createCredentail(user, database, pass);
	}
private MongoCredential createCredentail ( String group ) { final Setting setting = this . setting ; if ( null == setting ) { return null ; } final String user = setting . getStr ( "user" , group , setting . getStr ( "user" ) ) ; final String pass = setting . getStr ( "pass" , group , setting . getStr ( "pass" ) ) ; final String database = setting . getStr ( "database" , group , setting . getStr ( "database" ) ) ; return createCredentail ( user , database , pass ) ; }
创建{@link MongoCredential}，用于服务端验证<br>
此方法会首先读取指定分组下的属性，用户没有定义则读取空分组下的属性

@param group 分组
@return {@link MongoCredential}，如果用户未指定用户名密码返回null
@since 4.1.20