Supporting posting received comments to Micropub endpoint

[voxpelli]

For those who don't want to rely on javascript for displaying their received WebMentions and neither wants to pull them themselves from any of the API:s provided already a standard support for pushing them to a Micropub endpoint would be great.

It's something that @aaronpk is already more or less doing in his endpoint: https://github.com/aaronpk/webmention.io/blob/master/helpers/formats.rb#L80 Almost Micropub, but not really.

Would be great if our two endpoints supported the same API as eg. @dshanske was intrigued by that for use with WordPress. See chat logs: https://chat.indieweb.org/dev/2016-08-15#t1471278307859000

[aaronpk]

Here's an example of what webmention.io currently sends, as a JSON post: https://gist.github.com/aaronpk/bb8628da6bf54bf85aa17d637d365b61

[cweiske]

Known supports posting comments via micropub: idno/known#1535

Instead of a h-value of entry, annotation is used with the following properties:

• url
• content
• type (can be like or reply)
• username
• userurl
• userphoto