As you've learned, those are currently only available to built-in commands. However, as I was curious and wanted to know how those are done, I looked in the API and found out that the URLs are just formatted normally but have a special "protocol":
You asked me to remind you to “test”.
_<slack-action://BSLACKBOT/reminders/complete/D01234567/1234//0/0/5678|Mark as complete>
or remind me later: <slack-action://BSLACKBOT/reminders/snooze/D01234567/1234//0/0/5678/15|15 mins> [...]
Clicking on such a link results in an API request to method chat.action
, with the following parameters:
bot: BSLACKBOT
payload: reminders/complete/D01234567/1234//0/0/5678
token: xoxs-tokenhere-nowayiampostingithere
So it looks like those URLs have three parts:
<slack-action://BSLACKBOT/reminders/complete/[...]|Mark as complete>
slack-action://
: the "protocol" like prefix to let Slack know this is a chat action URL.
BSLACKBOT
: the bot which (who?) will receive the payload. Can only be a bot user and the ID must start with B, or the API request will fail with invalid_bot
.
- the rest of the URL: the payload that gets passed to the bot. It doesn't look like this is parsed nor handled specially by Slack.
This is actually not a new feature, since they used to have API URLs back in late 2013 or early 2014 (I don't remember precisely) which they removed for "security reasons".
It could be interesting to see if we can use chat actions with custom bots, and if so, what we could do with it.