Here's how to add the sameAs property to your author schema using the 'Schema & Structured Data for WP & AMP' WordPress plugin, whether your site has one author or many.
Schema & Structured Data for WP & AMP (or SASWP) is my current favourite plugin for adding schema to WordPress sites, not least because even the free version is pretty smart. For example, when you create a Schema Type and apply it to your content, the plugin will automatically add author schema if appropriate.
But it wasn't immediately obvious to me how to implement the sameAs property within this author schema, which Schema.org defines as the "URL of a reference Web page that unambiguously indicates the item's identity".
For author schema, sameAs is usually used to add the author's profiles on different sites and social media platforms, enabling search engines to build a more complete picture of the author.
In Schema & Structured Data for WP & AMP, the sameAs property is referred to as "Author Social Profile". That's a slightly misleading name, because sameAs isn't limited to social media - you could, for example, use SameAs to link to the author's Wikipedia page (if they have one).
The output of Author Social Profile accepts a comma-separated string of values, enabling you to set up multiple "sameAs" properties for a single author. How does that work in practice? Let's look at a couple of scenarios:
My website only has one author (me!), so setup is simple. I modified the schema output for my posts so that "Author Social Profile" has the following "Manual Text" value:
https://www.facebook.com/jamesdanielclark,https://twitter.com/technicallyprod,https://www.technicallyproduct.co.uk/about,https://bsky.app/profile/technicallyproduct.co.uk
This is me on various social media platforms as well as the About page of my own website (I don't have my own Wikipedia page!). And here's how that looks like this in the plugin's "Edit Schema Type" screen:
When I run it through Google's Rich Results Test tool I get a green tick indicating a valid item. Clicking into the details, I can see my sameAs values all listed out separately:
The above approach of setting a manual text value for "Author Social Profile" wouldn't be appropriate for multiple authors, as it would apply the same "sameAs" properties to all of them.
For a site with perhaps two or three authors, you could create a different Schema Type for each author in Schema & Structured Data for WP & AMP and set the Placement value to filter by Author. This would enable you to have a different modified schema output for each author:
However, this would become difficult to maintain on a site with a high number of authors or occasional contributors. In that scenario, it would be better to use a Custom Field for Author Social Profile (instead of Manual Text). I think you could use a plugin such as ACF or Ultimate Member to generate the custom field - though I haven't tried it myself in this context.
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