There are lot many pages on web as password protected. For example, if you are running a Moodle based e-learning platform then in most of the cases it asks for login ID and Password for entering in the system. Or if you are running a paid forum where people need to enter ID and password after purchasing the subscription for premium support. Now if you want to monetize from those protected areas or web pages using Google Adsense then you need to authenticate the Adsense Crawler to access those pages so that Google can server keyword based relevant ads. Google Adsense Crawler is different from Google Search Crawler and it doesn’t have any default ID and Password to access the data for cache purpose like Google Search Crawler.
To authenticate Google Adsense Crawler for accessing the data from protected areas, you need to use the option “Site Authentication” under Google Adsense Admin. Enter into your Google Adsense Account and go to Adsense Setup ==> Site Authentication. Now provide the details like Authentication URL i.e. the page (authentication page) where you need to enter User ID and Password. Choose the Authentication Method. If you are using any forum or Moodle like platform where you need to enter User ID and Password and Submit that then you need to select POST from the dropdown. If the page access is restricted from .htaccess file then you need to select .htaccess. GET option is in case your system passes values thru URL.
Now Enter the Attribute for User ID and Password and the values for the same. If you have added the site on Google Webmaster Tool with same email ID then no need for another verification but if not added then you will be redirected to Webmaster Tool for verification. You need to upload a file on root folder of the site for verification.
Done! Now Google Adsense Crawler can access the protected pages and show relevant ads on those pages.