I am planning on using Canvas to lightweight integrate an external web app. In the documentation (https://resources.docs.salesforce.com/218/latest/en-us/sfdc/pdf/canvas_framework.pdf) I wasn't able to find an example on how to send more heavyweight context data to the Canvas URL endpoint.
I need to seen not only user information but also the current record and a few child records (formatted as JSON) to the Canvas.
How would I do this?