C# Online Compiler | .NET Fiddle

//Written by Paul Seal. Licensed under MIT. Free for private and commercial uses.

using System;
using System.Text.RegularExpressions;
using CodeShare.Library.Passwords;
                    
public class Program
{
    public static void Main()
    {
        bool includeLowercase = true;
        bool includeUppercase = true;
        bool includeNumeric = true;
        bool includeSpecial = false;
        bool includeSpaces = false;
        int lengthOfPassword  = 16;
        
        string password = PasswordGenerator.GeneratePassword(includeLowercase, includeUppercase, includeNumeric, includeSpecial, includeSpaces, lengthOfPassword);
        
        while(!PasswordGenerator.PasswordIsValid(includeLowercase, includeUppercase, includeNumeric, includeSpecial, includeSpaces, password))
        {
            password = PasswordGenerator.GeneratePassword(includeLowercase, includeUppercase, includeNumeric, includeSpecial, includeSpaces, lengthOfPassword);
        }
        
        Console.WriteLine(password);
    }
}

namespace CodeShare.Library.Passwords
{
    public static class PasswordGenerator
    {
        /// <summary>
        /// Generates a random password based on the rules passed in the parameters
        /// </summary>
        /// <param name="includeLowercase">Bool to say if lowercase are required</param>
        /// <param name="includeUppercase">Bool to say if uppercase are required</param>
        /// <param name="includeNumeric">Bool to say if numerics are required</param>
        /// <param name="includeSpecial">Bool to say if special characters are required</param>
        /// <param name="includeSpaces">Bool to say if spaces are required</param>
        /// <param name="lengthOfPassword">Length of password required. Should be between 8 and 128</param>
        /// <returns></returns>
        public static string GeneratePassword(bool includeLowercase, bool includeUppercase, bool includeNumeric, bool includeSpecial, bool includeSpaces, int lengthOfPassword)
        {
            const int MAXIMUM_IDENTICAL_CONSECUTIVE_CHARS = 2;
            const string LOWERCASE_CHARACTERS = "abcdefghijklmnopqrstuvwxyz";
            const string UPPERCASE_CHARACTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
            const string NUMERIC_CHARACTERS = "0123456789";
            const string SPECIAL_CHARACTERS = @"!#$%&*@\";
            const string SPACE_CHARACTER = " ";
            const int PASSWORD_LENGTH_MIN = 8;
            const int PASSWORD_LENGTH_MAX = 128;

            if (lengthOfPassword < PASSWORD_LENGTH_MIN || lengthOfPassword > PASSWORD_LENGTH_MAX)
            {
                return "Password length must be between 8 and 128.";
            }

            string characterSet = "";
            
            if (includeLowercase)
            {
                characterSet += LOWERCASE_CHARACTERS;
            }

            if (includeUppercase)
            {
                characterSet += UPPERCASE_CHARACTERS;
            }

            if (includeNumeric)
            {
                characterSet += NUMERIC_CHARACTERS;
            }

            if (includeSpecial)
            {
                characterSet += SPECIAL_CHARACTERS;
            }

            if (includeSpaces)
            {
                characterSet += SPACE_CHARACTER;
            }

            char[] password = new char[lengthOfPassword];
            int characterSetLength = characterSet.Length;

            System.Random random = new System.Random();
            for (int characterPosition = 0; characterPosition < lengthOfPassword; characterPosition++)
            {
                password[characterPosition] = characterSet[random.Next(characterSetLength - 1)];

                bool moreThanTwoIdenticalInARow = 
                    characterPosition > MAXIMUM_IDENTICAL_CONSECUTIVE_CHARS
                    && password[characterPosition] == password[characterPosition - 1] 
                    && password[characterPosition - 1] == password[characterPosition - 2];

                if (moreThanTwoIdenticalInARow)
                {
                    characterPosition--;
                }
            }

            return string.Join(null, password);
        }
        
        /// <summary>
        /// Checks if the password created is valid
        /// </summary>
        /// <param name="includeLowercase">Bool to say if lowercase are required</param>
        /// <param name="includeUppercase">Bool to say if uppercase are required</param>
        /// <param name="includeNumeric">Bool to say if numerics are required</param>
        /// <param name="includeSpecial">Bool to say if special characters are required</param>
        /// <param name="includeSpaces">Bool to say if spaces are required</param>
        /// <param name="password">Generated password</param>
        /// <returns>True or False to say if the password is valid or not</returns>
        public static bool PasswordIsValid(bool includeLowercase, bool includeUppercase, bool includeNumeric, bool includeSpecial, bool includeSpaces, string password)
        {
            const string REGEX_LOWERCASE = @"[a-z]";
            const string REGEX_UPPERCASE = @"[A-Z]";
            const string REGEX_NUMERIC = @"[\d]";
            const string REGEX_SPECIAL = @"([!#$%&*@\\])+";
            const string REGEX_SPACE = @"([ ])+";

            bool lowerCaseIsValid = !includeLowercase || (includeLowercase && Regex.IsMatch(password, REGEX_LOWERCASE));
            bool upperCaseIsValid = !includeUppercase || (includeUppercase && Regex.IsMatch(password, REGEX_UPPERCASE));
            bool numericIsValid = !includeNumeric || (includeNumeric && Regex.IsMatch(password, REGEX_NUMERIC));
            bool symbolsAreValid = !includeSpecial || (includeSpecial && Regex.IsMatch(password, REGEX_SPECIAL));
            bool spacesAreValid = !includeSpaces || (includeSpaces && Regex.IsMatch(password, REGEX_SPACE));

            return lowerCaseIsValid && upperCaseIsValid && numericIsValid && symbolsAreValid && spacesAreValid;
        }        
    }
}

 
//Written by Paul Seal. Licensed under MIT. Free for private and commercial uses.
​
using System;
using System.Text.RegularExpressions;
using CodeShare.Library.Passwords;
                    
public class Program
{
    public static void Main()
    {
        bool includeLowercase = true;
        bool includeUppercase = true;
        bool includeNumeric = true;
        bool includeSpecial = false;
        bool includeSpaces = false;
        int lengthOfPassword  = 16;
        
        string password = PasswordGenerator.GeneratePassword(includeLowercase, includeUppercase, includeNumeric, includeSpecial, includeSpaces, lengthOfPassword);
        
        while(!PasswordGenerator.PasswordIsValid(includeLowercase, includeUppercase, includeNumeric, includeSpecial, includeSpaces, password))
        {
            password = PasswordGenerator.GeneratePassword(includeLowercase, includeUppercase, includeNumeric, includeSpecial, includeSpaces, lengthOfPassword);
        }
        