As part of the WMF Matrix trial (T230531: Run Matrix trial using the modular.im-hosted instance) bridge Matrix together with Slack so that Slack users can see and talk to Matrix users and vice versa.

• evaluate available bridge implementations (matrix-appservice-slack, matrix-puppet-slack, mx-puppet-slack; see also comparison here)
• evaluate security footprint (most crucially, will the bridge have access to everything in Slack or can it be limited to a set of rooms that opt in to the trial? Will it have access to non-public rooms it is not invited to?)
• set up the bridge on the Modular.im instance (or we could use a public bridge, based on the evaluation above)
• make sure that the Matrix integrations menu offers our choice of bridge, not the default bridge
• configure & test bridging