enterprise_id in InstallationQuery can be invalid for Slack Connect channel events

[seratch]

Bug Report

tl;dr - The fix for #687 was not complete for the events that happen in a Slack Connect channel shared among an Enterprise Grid workspace and non-Enterprise Grid workspace.

In a Slack Connect shared channel, the enterprise_id / team_id to use is always under the authorizations[0]. For instance, the following event is coming from workspace: T_this_non_grid_workspace, which is not in an Enterprise Grid.

{
  "team_id": "T_connected_grid_workspace",
  "enterprise_id": "E_org_id",
  "api_app_id": "A111",
  "event": {
    "type": "message",
    "text": ":wave: Hi, this is my first message in a Slack Connect channel!",
    "user": "U111",
    "ts": "1622099033.001500",
    "team": "T_this_non_grid_workspace",
    "channel": "C111",
    "channel_type": "channel"
  },
  "type": "event_callback",
  "authorizations": [
    {
      "enterprise_id": null,
      "team_id": "T_this_non_grid_workspace",
      "user_id": "U_authed_user",
      "is_bot": true,
      "is_enterprise_install": false
    }
  ],
  "is_ext_shared_channel": true,
  "event_context": "2-message-T_connected_grid_workspace-A111-C111"
}

In this case, the argument for installationStore#fetchInstallation includes an invalid enterprise_id.

const app = new App({
  developerMode: true,
  socketMode: true,
  appToken: process.env.SLACK_APP_TOKEN,
  logLevel: process.env.SLACK_LOG_LEVEL || LogLevel.DEBUG,
  signingSecret: process.env.SLACK_SIGNING_SECRET,
  clientId: process.env.SLACK_CLIENT_ID,
  clientSecret: process.env.SLACK_CLIENT_SECRET,
  stateSecret: 'my-state-secret',
  scopes: ['commands', 'chat:write'],
  installationStore: {
    storeInstallation: async (installation) => {
      // TODO
    },
    fetchInstallation: async (installQuery) => {
      console.log(installQuery);
      // TODO
    },
  },
});

The console.log(installQuery); prints the following:

{
  userId: 'U111',
  isEnterpriseInstall: false,
  teamId: 'T_this_non_grid_workspace',
  enterpriseId: 'E_org_id',
  conversationId: 'C111'
}

The enterpriseId must be null.

Reproducible in:

any version

node version:

any

Steps to reproduce:

1. Create a workspace that is not in an Enterprise Grid (T_this_non_grid_workspace)
2. Create a Slack Connect channel with a workspace in an Enterprise Grid (T_connected_grid_workspace)
3. Install your Slack app that subscribes message events to the T_this_non_grid_workspace workspace
4. Add the app to the Slack Connect channel
5. See the installationQuery in fetchInstallation method

Expected result:

The enterpriseId is null

Actual result:

The T_connected_grid_workspace workspace's enterprise_id is set.

What type of issue is this? (place an x in one of the [ ])

• bug
• enhancement (feature request)
• question
• documentation related
• example code related
• testing related
• discussion

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.