Cloud Functions for

• Slack - Slash commands (https://api.slack.com/slash-commands)
• Slack - Dialogs (https://api.slack.com/dialogs)

Google has a guide to Slack apps, but it is outdated and using Legacy tokens from Slack.
These Cloud Functions implement the newer and safer way for Slack apps to verify that the request comes from Slack: https://api.slack.com/docs/verifying-requests-from-slack

The Slack app should be configured to send a Slash command to the Google Cloud function under directory slash_command:

The Google Cloud function slash_command sends a short message to the user, and triggers a Slack dialog window:

Once the user responds to the dialog, Slack sends a request to the Cloud function under directory dialog_submission, which pushes the message containing the submission data and other data sent by Slack to into a topic on Google Cloud Pub/Sub.

Prequisite:

• You must have a Cloud Pub/Sub topic.
• You will also need to give the user running the Dialog Cloud Function write access to that topic.
• An app registered in Slack. This is required to get the signing secret and oauth token for deployment below.

Deploy the Cloud Functions:

Configure environment variables for the configurable options.

export slash_command=</YOUR-SLASH-COMMAND>
export pubsub_topic=projects/<YOUR-PROJECT>/topics/<YOUR-TOPIC>
export signing_secret=<YOUR_SIGNING_SECRET_FROM_SLACK>
export oauth_token=<YOUR_APPS_SLACK_OAUTH_ACCESS_TOKEN>

Slash command function:

cd src/slash_command
gcloud functions deploy slash_command --runtime python37 --trigger-http --memory=128MB --set-env-vars SLACK_SIGNING_SECRET=$signing_secret,SLACK_OAUTH_TOKEN=$oauth_token,SLACK_SLASH_COMMAND=$slash_command

Dialog handling function:

cd src/dialog_submission
gcloud functions deploy dialog_submission --runtime python37 --trigger-http --memory=128MB --set-env-vars PUBSUB_TOPIC_NAME=$pubsub_topic,SLACK_SIGNING_SECRET=$signing_secret