json middleware is part of Express v4.16.0

src/oidc.js

@@ -888,7 +888,7 @@ async function start() {
     app.set('views', path.join(__dirname, 'oidc_templates'));
     app.set('view engine', 'ejs');
 
-    const json = middleware.json({ strict: true, limit: '2mb' });
+    const json = express.json({ strict: true, limit: '2mb' });
     function setNoCache(req, res, next) {
         res.set('cache-control', 'no-store');
         next();