RandomString.cs

        public static string GenerateId(int length)
        {
            const string symbols = "abcdefghijklmnopqrstuvwxyz0123456789";

            byte[] buffer = null;

            try
            {
                buffer = ArrayPool<byte>.Shared.Rent(length);

                for (var i = 0; i < length; i++)
                {
                    var index = RandomNumberGenerator.GetInt32(length);
                    buffer[i] = (byte)symbols[index];
                }
                
                return Encoding.ASCII.GetString(buffer, 0, length);
            }
            finally
            {
                ArrayPool<byte>.Shared.Return(buffer);
            }
        }