return Stuff{ Prop1 = "a", Prop2 = 5 };

return ClientCredentials
{
  UserName.Password = "abc123",
  UserName.UserName = "server\user"
};

ClientCredentials clientCredentials = new ClientCredentials();
clientCredentials.UserName.UserName = "server\user";
clientCredentials.UserName.Password = "abc123";
return clientCredentials;

ClientCredentials CreateClientCredentials(String userName, String password) {
  var clientCredentials = new ClientCredentials();
  clientCredentials.UserName.UserName = userName;
  clientCredentials.UserName.Password = password;
  return clientCredentials;
}

public static class ClientCredentialsExtensions {

  public static ClientCredentials WithUserName(
    this ClientCredentials clientCredentials, String userName) {
    // Argument checking omitted.
    clientCredentials.UserName.UserName = userName;
    return clientCredentials;
  }

  public static ClientCredentials WithPassword(
    this ClientCredentials clientCredentials, String password) {
    // Argument checking omitted.
    clientCredentials.UserName.Password = password;
    return clientCredentials;
  }

}

var clientCredentials = new ClientCredentials()
  .WithUserName("username")
  .WithPassword("password");

var clientCredentials = new CreateClientCredentials("username", "password");