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Chapter 1: Overview of Content Policy Language
The Content Policy Language (CPL) is a programming language with its own concepts and rules that
you must follow.
This chapter provides an overview of CPL, including the following topics:
• "Concepts"
• "CPL Language Basics"
• "Writing Policy Using CPL"
• "Troubleshooting Policy"
• "Upgrade/Downgrade Issues"
Concepts
The term policy, as used here, refers to configuration values and rules applied to render decisions on
authentication requirements, access rights, quality of service, or content transformations (including
rewrites and off-box services that should be used to process the request or response). Often, the policy
references system configuration for the default values for some settings and then evaluates rules to see
if those settings should be overridden.
CPL is a language for specifying the policy rules for the ProxySG. Primarily, it controls the following:
• User Authentication requirements
• Access to Web-related resources
• Cache content
• Various aspects of request and response processing
• Access logging
You can create policy rules using either the Visual Policy Manager (VPM), which is accessible through
the Management Console, or by composing CPL.
Before reading sample CPL or trying to express your own policies in CPL, Blue Coat recommends that
you understand the fundamental concepts underlying policy enforcement in the ProxySG appliances.
This section provides an overview of important concepts.
Transactions
In the CPL context, a transaction is the encapsulation of a request for service and any associated
response for the purposes of policy evaluation and enforcement. In most cases, a transaction is created
for each unique request for service, and the transaction exists for the time taken to process the request
and deliver the response.
The transaction serves the following purposes:
• Exposes request and response state for testing during policy evaluation.