private static string RandomNumberGenerator(int length) 
{ 
    System.Security.Cryptography.RandomNumberGenerator rng = System.Security.Cryptography.RandomNumberGenerator.Create(); 

    char[] chars = new char[length]; 

    //based on your requirment you can take only alphabets or number 
    string validChars = "abcdefghijklmnopqrstuvwxyzABCEDFGHIJKLMNOPQRSTUVWXYZ1234567890"; 

    for (int i=0; i< length; i++) 
    { 
        byte[] bytes = new byte[1]; 
        rng.GetBytes(bytes); 
        
        Random rnd = new Random(bytes[0]); 

        chars[i] = validChars[rnd.Next(0,61)]; 
    }

    return (new string(chars)); 
}