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https://www.slideshare.net/wan2land/php-slack-bot
https://chatbotslife.com/write-a-serverless-slack-chat-bot-using-aws-e2d2432c380e
https://api.slack.com/slash-commands
https://api.slack.com/tutorials/aws-lambda
https://api.slack.com/slack-apps
http://www.usefulparadigm.com/2016/04/06/creating-a-slack-bot-with-aws-lambda-and-api-gateway/