Improve the logic to extract the requestUserId for context objects

[seratch]

While testing this new feauture, I found that the logic to set context.requestUserId can be improved for Events API patterns. I will make changes for it in a different pull request.

As I mentioned at #1144, bolt-java's user ID extration for context objects can be improved like bolt-python does.

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

• bolt (Bolt for Java)
• bolt-{sub modules} (Bolt for Java - optional modules)
• slack-api-client (Slack API Clients)
• slack-api-model (Slack API Data Models)
• slack-api-*-kotlin-extension (Kotlin Extensions for Slack API Clients)
• slack-app-backend (The primitive layer of Bolt for Java)

Requirements

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[lcf]

Hi @seratch , do I understand correctly that userId is not extracted at all for events?

This means that installationService and distributed applications will never work with Slack Bolt for Java, because this method
public Installer findInstaller(String enterpriseId, String teamId, String userId) will never be called, since there was no userId extracted.

If that is true, is it okay to change this to a bug?

[seratch]

The request user ID is set for many request patterns, but currently, it's indeed unset for Events API request patterns. This lack of data affects your app's behavior only if your app manages a user token for all request users. If your app only manages bot tokens, the mandatory findBot() method works without any issues even for Events API patterns.

Regarding request user IDs in the Events API patterns, improving like bolt-python does not guarantee that the requestUserId will always be set for all request patterns. It's unclear which user ID should be picked for many events. Also, due to the complexity and variation of event payload data structure, the extraction logic cannot be perfect in a simple way.

For a specific use case requiring a user token, this may be called a bug, but we think this is a minor improvement. So, unfortunately we don't have immediate plans to work on it. If you're in a hurry to use a user token corresponding to a request, please consider adding additional code on your listener function side and call the findInstaller() method using the user ID to receive the user's user token.

It'd be appreciated if you could understand this.

[lcf]

@seratch let's put user tokens aside. It does not work for many basic use cases as well. For example, a user opens home tab and we want to render some data for the current user. If we read ctx.getRequestUserId(), it is going to return null, even though:

1. It is supported and works fine in other SDKs, like Java Script.
2. We parse user id everywhere else in the Java SDK, just not for the events.

It is inconsistent, inconvenient and error prone.

We should copy these few lines: https://github.com/slackapi/bolt-js/blob/87d75c59f5eb9b28586173487dac1a0d6e1deada/src/App.ts#L1533

      if ('user' in event) {
        if (typeof event.user === 'string') {
          return event.user;
        }
        if (typeof event.user === 'object') {
          return event.user.id;
        }
      }

To EventRequest in Java SDK to fix the bug and achieve feature parity.
Do you agree @seratch ?