As a supplementary note, JetPack v4.5 now includes a Gravatar widget which functions a lot like the H-card Widget and pulls in data from the user's profile as well as their Gravatar account. Now, if only it had microformats...

Since the code and UI may be worth looking at: https://github.com/Automattic/jetpack/tree/master/modules/widgets

Announcement: https://jetpack.com/2017/01/17/jetpack-4-5-monetize-your-site-brand-new-videopress-and-many-many-new-shortcodes/