Index: src/middleware/render.js
===================================================================
--- src/middleware/render.js	(revision 834bcc3c41c52321679550863b74ca035538659f)
+++ src/middleware/render.js	(revision dd1028af6e9c6676e6c93734784524e86e57a3d6)
@@ -137,4 +137,6 @@
     cspNonce: () => '',
     currentPath: req.path,
+    // Absolute origin (for building absolute URLs like the generated og:image).
+    ogOrigin: (process.env.PUBLIC_BASE_URL || `${req.protocol}://${req.get('host') || ''}`).replace(/\/+$/, ''),
     ...data,
   };