This looks pretty straightforward, especially for single-author blogs. And it’s a lightway way to bridge Write.as’s limited fediverse features. With author byline indicators, people who respond to a blogpost on the fediverse can also reply to the author’s account on a service which has deeper support for that sort of thing.
Eugen has indicated that this feature no longer requires manual opt-in:
Actually, this is a quirk of how we implemented the feature to get it launched quickly on Write.as. To fix it, you’ll need to enter your fediverse @ handle in the Verification field (e.g. @amoroso@fosstodon.org). When you save your settings, it will turn back into the URL, but we’ll have the data we need to correctly display the fediverse:creator tag.
Once you do this, note that Mastodon also might not show the author attribution without a large preview image. This is just how they do things on their end. So if you don’t normally add photos in your posts, a good way to handle this is to add a large (e.g. 1200x630 pixels) “Social Image” on your blog’s Customize page.
I re-entered my fediverse handle, uploaded a 1400x1400 Social Image, published a post with a 1920x1080 image, and shared the post on Mastodon. The Mastodon post still doesn’t have the author byline.
I published another post and, although both the post and the blog apparently fulfill the requirements, there’s still no byline when sharing on Mastodon. I don’t know what’s wrong with my setup.