[core] Domain-specific data correlation between workflow and events (stretch goal)

Motivation

Knative Eventing is a serverless platform that enables developers to create event producers and consumers for their applications. Knative Eventing uses standard HTTP POST requests to send and receive events between event producers and consumers. These events conform to the CloudEvents specification, which enables creating, parsing, sending, and receiving events in any programming language.

Goal

Enable events to trigger specific workflows based on its payload

Scenarios

As a developer, I need to address workflow(s) via domain-specific values in data when sending an event so that the event is consumed only by active workflows which contain that domain-specific value in data.

Expected outcomes

Workflow instances are correlated with incoming events via workflow identifier or workflow data
Correlation attributes are set only using events, i.e. a workflow instance has to have event state as a start

Correlation of events (between events) is out of scope - that’s for complex event processing
Setting correlation attributes using a REST request (e.g. when the operation state is a start) is out of scope