title: slack doesn't recognize github webhook payload format
body: <p>I'm trying to create a slack app that uses incoming webhooks. I want my github repository to post to slack whenever the wiki is updated. I believe I've set up the webhook on github just fine, because I can see that it is attempting a delivery whenever I update the wiki. However, there's always the error, "no_text". I think this error means slack is expecting an item named "text," but the payload from github provides none. I verified this by trying two curl commands from the command prompt (I'm on windows):</p>
  
  <p><code>curl -X POST -H "Content-type: application/json" --data "{\"text\":\"Hello, World!\"}" [MY_WEBHOOK_URL]</code><br>
  <code>curl -X POST -H "Content-type: application/json" --data "{\"foobar\":\"Hello, World!\"}" [MY_WEBHOOK_URL]</code></p>
  
  <p>This first one works as expected; the message "Hello, World!" gets posted to the slack channel I wanted, and I got back the "ok" message from curl. The second one did not work; the message was not posted, and I got back the message "no_text" from curl.</p>
  
  <p>I can think of two possible solutions to this problem:</p>
  
  <ol>
  <li>Change the format of the payload coming from github to include an item called "text" and other properties slack actually recognizes.</li>
  <li>Get slack to recognize the format the payload is already in, perhaps by telling it to post the contents of a property other than "text."</li>
  </ol>
  
  <p>I don't know how to accomplish either of these, or if they're even possible. Or perhaps there's another solution I haven't thought of?</p>
  
  <p>Note: I already tried to use the github slack app, but couldn't figure out how to get it to post updates to the wiki. (See my other question if you'd like: <a href="https://stackoverflow.com/questions/43076734/slack-github-integration-doesnt-find-wiki-repository">slack github integration doesn&#39;t find wiki repository</a>)</p>