LinqPad.RandomString

public static string GenerateRandomString(int length = 10)
{
  const string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmopqrstuvwxyz";
  
  var r = new Random();
  
  return new string(Enumerable.Repeat(alphabet, length)
                              .Select(s => s[r.Next(s.Length)])
                              .ToArray());
}