Previewing the Secure Page in Sitecore

Previewing the Secure Page in Sitecore
PREVIEW AS ANONYMOUS

<setting name="Preview. AsAnonymous" value="true" />
           The above setting specifies whether Sitecore will use the Anonymous user account when you   preview an item.
           If true, Sitecore uses the Anonymous user account when you preview an item.
           If false, Sitecore uses the current user account when you preview an item.
           Default value: true
The above setting and and information provided by sitecore you will find in AppConfig\Sitecore.config file.