Original

gistfile1.cs

Outcome<string> IAuthenticationService.ValidatePassword(IDssPrincipal dssPrincipal, string password)
{
    const int minimumLength = 8;
    const int maximumLength = 20;
    const string specialCharactersPattern = @"\#\$\%\&\@\*\+\-\=\!\.\?\:\;\(\)\[\]\{\}\^\~_";

    var observations = new List<string>();
    var email = dssPrincipal.Identity.EmailAddress.ToMaybe();

    // Password must not be null
    if (string.IsNullOrWhiteSpace(password))
    {
        return Outcome.Failure("Password cannot be empty");
    }

    // Password must have at least 8 characters
    if (password.Length < minimumLength)
    {
        observations.Add(string.Format("Password must be at least {0} characters", minimumLength));
    }

    // Password must have no more than 20 characters
    if (password.Length > maximumLength)
    {
        observations.Add(string.Format("Password cannot be longer than {0} characters", maximumLength));
    }

    // Password must not contain a substring of the user's email
    if (email.HasValue && email.Value.IndexOf(password, StringComparison.InvariantCultureIgnoreCase) > -1)
    {
        observations.Add("Password cannot contain parts of the email address associated with this account.");
    }

    // Password must not contain spaces
    if (Regex.IsMatch(password, @"\w+"))
    {
        observations.Add("Password cannot contain spaces");
    }

    // Password must not contain prohibited characters
    if (Regex.IsMatch(password, @"[^" + specialCharactersPattern + @"]+"))
    {
        observations.Add("Password contains prohibited characters");
    }

    // Password must have at least two classes of characters (e.g., letters, digits, "allowed specials").
    var characterClasses = 0;
    characterClasses += Regex.IsMatch(password, @"[a-zA-Z]+") ? 1 : 0;
    characterClasses += Regex.IsMatch(password, @"\d+") ? 1 : 0;
    characterClasses += Regex.IsMatch(password, @"[" + specialCharactersPattern + @"]+") ? 1 : 0;
    if (characterClasses < 2)
    {
        observations.Add("Password must contain at least two kinds of characters (letters, numbers or 'allowed special characters'.");
    }

    return observations.Any() ? Outcome.Failure(observations.AsEnumerable()) : Outcome.Success();
}