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Conventions

By convention, any interceptor CFC must create a method with the same name as the event they want to listen to. This method has a return type of boolean and receives 5 arguments. So let's explore their rules.

boolean function {point}( event, data, buffer, rc, prc );

Arguments

event which is the request context object
data which is a structure of data that the broadcaster sends
buffer which is a request buffer object you can use to elegantly produce content that is outputted to the user's screen
rc reference to the request collection struct
prc reference to the private request collection struct

Return type

The intercepting method returns boolean or void. If boolean then it means something:

True means break the chain of execution, so no other interceptors in the chain will fire.
False or void continue execution

component extends="coldbox.system.Interceptor"{

    function configure(){}

    boolean function afterConfigurationLoad(event,data,buffer){
        if( getProperty('interceptorCompleted') eq false){
            parseAndSet();    
            setProperty('interceptorCompleted',true);
        }

        return false;
    }
}

Also remember that all interceptors are created by WireBox, so you can use dependency injection, configuration binder's, and even AOP on interceptor objects. Here is a more complex sample:

HTTP Security Example:

/**
* Intercepts with HTTP Basic Authentication
*/
component {

    // Security Service
    property name="securityService" inject="id:SecurityService";

    void function configure(){
        if( !propertyExists("enabled") ){
            setProperty("enabled", true );
        } 
    }

    void function preProcess(event,struct data, buffer){

        // verify turned on
        if( !getProperty("enabled") ){ return; }

        // Verify Incoming Headers to see if we are authorizing already or we are already Authorized
        if( !securityService.isLoggedIn() OR len( event.getHTTPHeader("Authorization","") ) ){

            // Verify incoming authorization
            var credentials = event.getHTTPBasicCredentials();
            if( securityService.authorize(credentials.username, credentials.password) ){
                // we are secured woot woot!
                return;
            };

            // Not secure!
            event.setHTTPHeader(name="WWW-Authenticate",value="basic realm=""Please enter your username and password for our Cool App!""");

            // secured content data and skip event execution
            event.renderData(data="<h1>Unathorized Access<p>Content Requires Authentication</p>",statusCode="401",statusText="Unauthorized")
                .noExecution();
        }    

    }    

}