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Writing Apache Modules with Perl and C by Lincoln Stein, Doug MacEachern

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6.5. Cookie-Based Access Control

The next example is a long one. To understand its motivation, consider a large site that runs not one but multiple web servers. Perhaps each server mirrors the others in order to spread out and reduce the load, or maybe each server is responsible for a different part of the site.

Such a site might very well want to have each of the servers perform authentication and access control against a shared database, but if it does so in the obvious way, it faces some potential problems. In order for each of the servers to authenticate against a common database, they will have to connect to it via the network. But this is less than ideal because connecting to a network database is not nearly so fast as connecting to a local one. Furthermore, the database network connections generate a lot of network overhead and compete with the web server for a limited pool of operating-system file descriptors. The performance problem is aggravated if authentication requires the evaluation of a complex SQL statement rather than a simple record lookup.

There are also security issues to consider when using a common authentication database. If the database holds confidential information, such as customer account information, it wouldn't do to give all the web servers free access to the database. A break-in on any of the web servers could compromise the confidentiality of the information.

Apache::TicketAccess was designed to handle these and other situations in which user authentication ...

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