Add support for Slack app

[dmitriishaburov]

Closes #244

Add token support for Slack notification provider, combined with configuring webhook url to https://slack.com/api/chat.postMessage will allow to send notifications as Slack App.

Do I need to write documentation for Slack notification provider?
Currently project doesn't have any, so it won't be clear that Slack apps are supported.

[dmitriishaburov]

@stefanprodan @phillebaba I'm sorry to ping you guys, but is this PR blocked by something, or is there something I can do?

[stefanprodan]

@dmitriishaburov can you please add a Slack App section to the API docs here: https://github.com/fluxcd/notification-controller/blob/main/docs/spec/v1beta1/provider.md#example

[stefanprodan]

@dmitriishaburov have you tested this? How did you generated the token? can the same token be used to post to different channels?

[dmitriishaburov]

@stefanprodan thanks, will update docs soon.

have you tested this?

Only by building docker image and running it in our cluster, checking that both webhook and app methods working properly.

How did you generated the token?

• Go to https://api.slack.com/
• Create an app -> From scratch
• Add chat:write token scope
• Install app into your workspace
• You'll get Bot User OAuth Token
• Invite app to your channel to allow it to post.

can the same token be used to post to different channels?

Yes, that's the main reason behind PR - you can use same set of credentials to post into different channels.

One main issue - Slack is ignoring the username field right now, so all messages posted from app username, losing the source-controller, kustomize-controller, etc username.
I will check if it's possible to avoid.

Edit: here's an example from Grafana docs, which supports Slack app https://grafana.com/docs/grafana/latest/alerting/old-alerting/notifications/#slack

[stefanprodan]

@dmitriishaburov thanks for answering my questions. I think the token generation steps and the username omission should be added to the docs along with an example.

[rjhenry]

+1 for this - anything I can do to help, let me know.

[dmitriishaburov]

Sorry for being lost for a while.

• Rebased onto latest main
• Updated provider.md docs
• Removed unused token field from SlackPayload

Did some research on username omission with Slack app. Although it is possible to grant apps rights to change username, that brings:

• Extra step to grant that rights
• Security concerns of app being able to impersonate every user and change avatars

Probably it's better to avoid this functionality.

Also there is minor (or not?) issue.
If you change the slack secret from webhook to slack app, notification-controller is not able to send message to Slack until restart. Don't know how to fix that, probably issue somewhere in reload functionality, or known issue (?)

[stefanprodan]

If you change the slack secret from webhook to slack app, notification-controller is not able to send message to Slack until restart.

We read the secret from Kubernetes API each time https://github.com/fluxcd/notification-controller/blob/main/internal/server/event_handlers.go#L143 but the client has an internal cache. Please open an issue if the failure persists.

[stefanprodan]

LGTM

Thanks @dmitriishaburov 🏅