Macaroon.prepare_for_request

You're seeing just the function prepare_for_request, go back to Macaroon module for more information.
Link to this function

prepare_for_request(discharge_macaroon, macaroon)

Specs

This prepares a Macaroon for delegation to another third-party authorization service. Returns a "protected" (or bound) discharge Macaroon.

discharge_macaroon - The Macaroon that will be sent to the third-party service.

macaroon - The Macaroon that the discharge_macaroon will be bound to. (The "root" Macaroon)