Untitled

public static string GetRandomString(int desiredLength, string characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
{
    var stringChars = new char[desiredLength];
    for (int i = 0; i < desiredLength; i++)
    {
        stringChars[i] = characters[_random.Next(characters.Length)];
    }
    return new string(stringChars);
}