One of the most common practices among Web site owners is providing links to other sites. Some Web pages consist almost entirely of links to other sites.
While many Web site owners welcome all exposure to their information, others have ownership and cost issues that require them to limit which other sites can provide links (referred access) to their content.
The most common mechanism for limiting referred access utilizes the referer (note the misspelling) header which all browser requests contain.
When a user enters a target URL in a browser, the request doesn't contain a referer header. When the user clicks a link to this same target URL, the requesting browser includes the referring URL (for the page containing the link) in a referer header in the resulting request.
By requiring that referring URLs be validated against a list of approved URLs, Web site administrators can limit referred access to their content.
This chapter describes how to use Excelerator's referer header validation feature to control access to cached content.