SlackAPPに登録する

Appを作成
Slack API: Applications | Slack
Tokenと権限を付与
メニューから OAuth & Permissions を選択
OAuth Access Tokenを確認する
下部のScopesから権限を付与

今回はチャンネルリスト取得なので下記権限

Access user’s public channels
channels:history

Access information about user’s public channels
channels:read
chat:write:bot

APIを確認する
channels.list method | Slack

Method URL:	https://slack.com/api/channels.list
Preferred HTTP method:	GET
Accepted content types:	application/x-www-form-urlencoded


Argument	Example	Required	Description
token	xxxx-xxxxxxxxx-xxxx	Required	
Authentication token bearing required scopes.

データを取得する

Jsonで取得(Ruby)

require 'net/http'
require 'uri'
require "json"
require 'pp'

res = Net::HTTP.get(URI.parse('https://slack.com/api/channels.list?token=xxxx-xxxxxxxxx-xxxx'))


hash = JSON.parse(res)
channels = hash["channels"]
channels.map { |channel| puts "##{channel["name"]}" }