Jack Chou in the official Adsense blog announces the launch of Site authentication.
With Site Authentication, Adsense's crawler can access your pasword protected webpages. Now all you have to do is provide it with a username and a password and the crawler will spider your site while also suggesting relevant ads.
The AdSense Help Center tells you how to let the crawler access your login-protected page:
To create authentication parameters for your pages, follow the steps below. Most of the steps require you to take action using the Sitemaps and Webmaster resources provided below:
- Create an authentication rule by accessing the Site Authentication feature in your account, located under the AdSense Setup tab.
- Log into Sitemaps using your Google Account. You must be using your Google Account in order for any changes you make in Sitemaps to be reflected in your AdSense account.
- Add a site to your account by following these instructions.
- After you've followed the instructions, on the next page, choose the Verify your site link under the >> Next step section. If you can't find it, then go back to the Sitemaps homepage and then follow these directions.
- If you're having problems, see the Webmaster Help entry on errors for assistance.
To learn more about verification in general, see the Webmaster Help Center.
However, is Site Authentication is not in your account, it is likely that you haven't changed your AdSense login to a Google Account. For this, update your login.
For more on site authentication, read the post.