How to add Slack message button to open direct chat with a user?

Question

I have a Slack bot that needs to return a message that includes list of Slack users and a button to direct message each user.

I want the engagement experience to stay consistent for the user. If the user is interacting with the bot via a desktop Slack app then I want the user to stay within the app (not to be taken away to the web client -- where they likely aren't authenticated).

Something like:

Results:

User A - click link to view User A's profile in Slack
[Message] - click button to open direct message with user A

User B - click link to view User B's profile in Slack
[Message] - click button to open direct message with user B

I'm stuck on a couple of issues:

1. How to link to a user's profile because I don't know if they are using the Slack app or Slack web (thus how to decide between showing slack://user?team=&id=.. or domain.slack.com/team/{id} approach? This is assuming I use either the title_link or author_link property.

2. How to create a message button that will open a direct message to a user (and even better open it and pre-populate a message)? I've currently been playing with a link action but have not had any luck.

I imagine I could workaround it by having the bot send the DM and then @mention the original user. Not great from the UX perspective.

UPDATE

Thanks to comments from Adil and Erik I think I have the best possible solution. I ended up crafting a message attachment for each result as follows:

    {
        "fallback": `${user['name']} likes pizza`,
        "text": `<@${user['uid']}>`,
        "actions": [
          {
            "type": "button",
            "text": "View Pizza Profile",
            "url": url(`/directory/${user['id']}`),
            "style": "primary"
          },
          {
            "type": "button",
            "text": "Order Pizza",
            "url": `https://slack.com/app_redirect?channel=${user['uid']}`
          }
        ]
    }

This solution provides:

• Text field which includes an @mention to the user (clicking it brings up the profile in the browser or native). It uses the text as the message header (and drops the author and title fields).
• Link action button to open a direct message chat via app_redirect

There are a couple of serious limitations:

1. For native, the direct message link causes a browser to open and then (if the user decides) redirects back to the app.
2. The user MUST be using a browser window that is already authenticated to the same workspace as the native client (this is a huge problem for UX as many individuals have multiple workspaces open, in which case the redirect fails with a non-obvious error message).

Answer 1

Adding to Adil's great answer about linking to a user profile

Here is how to provide a link to open a direct message between the current and another user:

You can use Slack's channel redirect feature to create a link that will open any channel for a user. This also works with direct message channels by providing the ID of the target user.

Example for user U12345678:

https://slack.com/app_redirect?channel=U12345678

You can provide this link via Link button or text link.

Note that this will always open a new browser tab/window though, even if the user is using a Slack native client (and no, there is no way to find out if the user it using a native client or the browser).

Another approach would be to just provide the user-mention in your message and let the user click on it to get a menu which includes "Direct Messages". This will work with every user and on every platform / client type:

Just include a standard user mention in your text with some instructions to the user:

<@U12345678>