Slack Events API

To help you implement Slack Events API listener, Slack Morphism provides you:

• Well-typed events model and ready to use JSON encoder/decoders
• Slack events signature verifier, to verify requests from Slack with confidence using your signing secret
• Additional Web API client methods to post replies to events back

Because Slack Morphism is a Web-framework agnostic, you are free to choose any you’re familiar with.

However, to simplify understanding and show how to use it, Slack Morphism provides full-featured bots for Akka HTTP and http4s, which implement Events API with OAuth.

Slack Events API Model

There are following types of Events

• SlackPushEvent for all push events (like incoming messages, opening tabs, installing/uninstalling app, etc)
• SlackInteractionEvent for all interaction events from Slack (actions on messages and views)

JSON encoders and decoders for Circe available either using

import org.latestbit.slack.morphism.codecs.implicits._

or using a trait:

trait MyHttpRoutesSupport extends org.latestbit.slack.morphism.codecs.CirceCodecs {
  ...
}

and you can decode all of the Slack Events like:

    decode[SlackInteractionEvent]( requestBody ) match {
      case Right( event ) => // ...
      case Left( ex ) => {
        logger.error( s"Can't decode push event from Slack: ${ex.toString}\n${requestBody}" )
        complete( StatusCodes.BadRequest )
      }
    }

Reply to Slack Events using response_url

There are some Slack events that provide you a response_url, and you can post a message back using the specified url from those events.

To help with these scenarios, you can use SlackApiClient.events.reply(), which doesn’t require any tokens to work:

client.events
    .reply(
      response_url = response_url,
      reply = SlackApiEventMessageReply(
        text = template.renderPlainText(),
        blocks = template.renderBlocks(),
        response_type = Some( SlackResponseTypes.EPHEMERAL )
      )
    )

To find out how to create a SlackApiClient instance read this.

Slack events signatures verifier

To verify requests from Slack using your signing secret, there is SlackEventSignatureVerifier, which provides you verify():

To verify event request you need:

• A complete HTTP request body
• The following HTTP headers from request (header names constants):
  • SlackEventSignatureVerifier.HttpHeaderNames.SignedTimestamp
  • SlackEventSignatureVerifier.HttpHeaderNames.SignedHash
• Your signing secret from your Slack app profile

val signatureVerifier = new SlackEventSignatureVerifier()

signatureVerifier.
    verify(
        config.signingSecret, 
        receivedSignedHash, 
        receivedSignedTimestamp, 
        requestBody
    ) match {
        case Right(success) => // the signature is verified
        case Left(err) => // absent or wrong signature    
    }