Add back checkBlacklist middleware

server/middleware/checkBlacklist.js

@@ -0,0 +1,12 @@
+function checkBlacklist(blacklist) {
+  return function (req, res, next) {
+    // Do not allow packages that have been blacklisted.
+    if (blacklist.includes(req.packageName)) {
+      res.status(403).type('text').send(`Package "${req.packageName}" is blacklisted`)
+    } else {
+      next()
+    }
+  }
+}
+
+module.exports = checkBlacklist