Add a /choose command to your workspace.

• /choose
  Choose one person from the current channel.
• /choose 3
  Choose three people from the current channel.
• /choose 3 from #general
  Choose three people from the general channel.
• /choose 3 from @foo @bar @baz @qux
  Choose three people of the four.

Go to the your Slack Apps web page.

1. Create New app.
2. Setup application.

• App Name: As you like.
• Development Slack Workspace: Select a workspace you want to install this app.

3. Create App.

In the new application page:

1. Select Slack Commands from Features menu.
2. Create New Command.
3. Setup new command.

• Command: /choose
• Request URL: Your Heroku application's URL.
• Short Description: e.g. "Choose some people".
• Usage Hint: e.g. "3 from #general".
• Escape channels, users, and links sent to your app: check

4. Save.

In the application page:

1. Select OAuth & Permissions from Features menu.
2. Add channels:read permission in Select Permission Scopes.

Select OAuth & Permissions from Features menu:

1. Install App to Workspace.
2. Authorize.

In the application page:

1. Select Basic Information from Settings menu.
2. Note down Verification Token.
3. Select OAuth & Permissions from Features menu.
4. Note down OAuth Access Token.

In the Heroku application's settings page:

5. Select Reveal Config Vars.
6. Add Verification Token as VERIFICATION_TOKEN.
7. Add OAuth Access Token as OAUTH_TOKEN.

MIT