How to Generate Access Token in C#

In C#, you can use classes from the System.Security.Cryptography namespace to generate a secure random token. Here is an example of a C# method that emulates the functionality of the JavaScript function you provided:

using System;
using System.Text;
using System.Security.Cryptography;

public class TokenGenerator
{
    public static string GenerateToken(int length, bool uppercase = true, bool lowercase = true, bool numbers = true)
    {
        const string uppercaseChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        const string lowercaseChars = "abcdefghijklmnopqrstuvwxyz";
        const string numberChars = "0123456789";

        var charset = new StringBuilder();
        if (uppercase) charset.Append(uppercaseChars);
        if (lowercase) charset.Append(lowercaseChars);
        if (numbers) charset.Append(numberChars);

        if (charset.Length == 0)
        {
            throw new ArgumentException("At least one character set must be selected.");
        }

        var token = new StringBuilder();
        using (var rng = new RNGCryptoServiceProvider())
        {
            byte[] uintBuffer = new byte[1];
            for (int i = 0; i < length; i++)
            {
                rng.GetBytes(uintBuffer);
                uint randomIndex = (uint)(uintBuffer[0] % charset.Length);
                token.Append(charset[randomIndex]);
            }
        }

        return token.ToString();
    }
}

// Example usage:
// string token = TokenGenerator.GenerateToken(16, true, true, true);

The GenerateToken method accepts four parameters: length (the length of the token), and three boolean parameters uppercase, lowercase, and numbers, which respectively indicate whether to include uppercase letters, lowercase letters, and numbers. If these parameters are not specified, they default to true.

Inside the method, we first construct a character set charset that includes all possible characters. Then, we use the RNGCryptoServiceProvider class to generate a secure random number; this class is part of the System.Security.Cryptography namespace. For each character of the token, we generate a random byte and use it to select a character from charset.

Please note that RNGCryptoServiceProvider is a cryptographically secure random number generator suitable for scenarios requiring high security. If your application does not require such a high level of security, you can use the Random class, but please be aware that Random is not cryptographically secure and may not be suitable for all purposes.