Currently, there's no way to configure slack token as described in this SO question.
I want to reevaluate this soon.
I believe the only issue here is that the portal doesn't easily allow us to set a key. I'll test this and create a Portal UX issue to track. Keeping this open just in case there are additional issues that pop up.
Steps to test slack token
So there are two issues before we can light up proper support for Slack in Functions.
Once those two have lit up, we can add it back to the bindings.json - https://github.com/Azure/azure-webjobs-sdk-templates/blob/dev/Bindings/bindings.json
So that said, this is going to become a feature planning issue, and I'm going to triage it to next considering that is where its dependencies are triaged.
I'd like to include this in "should-have" since I hope it's relatively low hanging fruit which results in big user impact. It's basically a bug of an existing feature.
Maybe we need a way to tag such 'should have' in GitHub issues?
I have one rc:should-have. I just thought I should discuss it first. :)
Will be addressed by this: https://github.com/projectkudu/AzureFunctionsPortal/issues/360
This is done now! :)