MOBILE_API/Common/Helper/PasswordGenerator.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace Common.Helper
{
    public class PasswordGenerator
    {
        public class PasswordOptions
        {
            public int RequiredLength { get; set; }
            public int RequiredUniqueChars { get; set; }
            public bool RequireLowercase { get; set; }
            public bool RequireDigit { get; set; }
            public bool RequireUppercase { get; set; }
            public bool RequireNonAlphanumeric { get; set; }

        }
        public static string GenerateRandomPassword(PasswordOptions opts = null)
        {
            if (opts == null) opts = new PasswordOptions()
            {
                RequiredLength = 8,
                RequiredUniqueChars = 4,
                RequireDigit = true,
                RequireLowercase = true,
                RequireNonAlphanumeric = true,
                RequireUppercase = true
            };

            string[] randomChars = new[] {
                "ABCDEFGHJKMNPQRSTUVWXYZ",    // uppercase 
                "abcdefghjkmnpqrstuvwxyz",    // lowercase
                "23456789",                   // digits
                "@#"                        // non-alphanumeric
            };
            string[] randomChars1 = new[] {
                   // uppercase 
                "abcdefghjkmnpqrstuvwxyz",    // lowercase
                "23456789",                   // digits
                                    // non-alphanumeric
            };
            Random rand = new Random();
            List<char> chars = new List<char>();

            if (opts.RequireUppercase)
                chars.Insert(rand.Next(0, chars.Count),
                    randomChars[0][rand.Next(0, randomChars[0].Length)]);

            if (opts.RequireLowercase)
                chars.Insert(rand.Next(0, chars.Count),
                    randomChars[1][rand.Next(0, randomChars[1].Length)]);

            if (opts.RequireDigit)
                chars.Insert(rand.Next(0, chars.Count),
                    randomChars[2][rand.Next(0, randomChars[2].Length)]);

            if (opts.RequireNonAlphanumeric)
                chars.Insert(rand.Next(0, chars.Count),
                    randomChars[3][rand.Next(0, randomChars[3].Length)]);

            for (int i = chars.Count; i < opts.RequiredLength
                || chars.Distinct().Count() < opts.RequiredUniqueChars; i++)
            {
                string rcs = randomChars1[rand.Next(0, randomChars1.Length)];

                chars.Insert(rand.Next(0, chars.Count),
                    rcs[rand.Next(0, rcs.Length)]);
            }

            return new string(chars.ToArray());
        }
    }
}