Feature

companion object Feature : 
    ApplicationFeature<ApplicationCallPipeline, Configuration, CallId>

Installable feature for CallId

key	`val key: AttributeKey<CallId>` Unique key that identifies a feature
phase	`val phase: PipelinePhase` ApplicationCallPipeline’s phase which this feature will be installed to

fun install(
    pipeline: ApplicationCallPipeline, 
    configure: Configuration.() -> Unit
): CallId

Feature installation script