HTML and CSS validation on a site that's password protected?

HI everyone,

I need to test the accessibility of an online email app and another portion
of a website that is only accessed after one logins. How can one test using
something like www.achecker.ca if the content needs a username/password?
Definitely need to do some CSS and HTML validation, but again cant really
just paste the URL into the form since it wouldn't have proper credentials.

I hope this makes sense and any help you could offer would be greatly
appreciated.
Regards
-PJ