Does Marketo have the ability to create private landing pages?

There's no reason why your pages can't look like Marketo pages no matter where they are. In fact, good web design would be to create a seamless transition and the user never realizes they switched servers.

If you really want password protected, I would look outside Marketo. This is a good program but it's power is in creating Marketing programs, not content portals. You can have APIs that share info between the two, but clearly this type of functionality is not Marketo's intended purpose nor in it's wheelhouse.

While Marketo doesn't offer a way to offer secured/password-protected pages, there are some techniques you can use to semi-restrict your LPs.  Establish a common password that would be required to access these pages. Then create a custom field for your password.

You will be creating three landing pages:

1. Login page (with javascript)
2. Unsuccessful login page (a static page to direct users to when the wrong password is submitted)
3. Success page (where the private content exists) (with javascript)

Create a program and include these local tokens (text):

Create a simple form with this new  custom "password" field and place it on your "login" LP:

Add the following js to this page (note, your "document.cookie" value will be unique to your instance):

<script language="javaScript" type="text/javascript">
<!--- PASSWORD PROTECTION SCRIPT
function TheLogin() {
var password = '{{my.Landing Page Password}}';
if (this.document.login.pass.value == password) {
  var sessionTimeout = 1; //hours
  var loginDuration = new Date();
  loginDuration.setTime(loginDuration.getTime()+(sessionTimeout*60*60*1000));
  document.cookie = "AvanadeLPSession=Valid; "+loginDuration.toGMTString()+"; path=/";
  top.location.href="https://{{my.Landing Page URL}}";
}
else {
  location.href="https://{{my.Unsuccessful Login Page URL}}";
  }
}
// End hiding --->
</script>

On your success page, include the following js:

<script language="javaScript" type="text/javascript">
// Check to see is login cookie is set - if not, redirect to login page
if (document.cookie.indexOf("AvanadeLPSession=Valid") == -1) {
  location.href = "https://{{my.Login Page URL}}";
}
</script>

Thanks to @Sanford Whiteman​ for assisting with some of this javascript.

I would use a segment here to define dynamic content. The non-customer traffic can then see different content.