The main authentication flow for Toolhub is an OAuth 2.0 handshake with metawiki. This is an interactive flow that is meant for human interaction.
The Toolhub API has a secondary authentication flow in the form of an OAuth 2.0 handshake with Toolhub itself. This is also an interactive flow that is meant for human interaction, but it generates tokens which can be renewed without human intervention. It is suited for use by a web service which is providing some value added interaction with the write API actions.
A third currently unsatisfied use case is a Toolhub API authentication method that can be used to run a bot as the bot developer's own user. Essentially the need is for a https://www.mediawiki.org/wiki/Manual:Bot_passwords or https://www.mediawiki.org/wiki/OAuth/Owner-only_consumers workalike method which can be used by bot operators.