Add Helmet to protect against common web vulnerabilities

Change-Id: I04329eb8a41c06b74a25ae47281f9b3bde7fc391
diff --git a/server/package.json b/server/package.json
index a3a4c8a..6d17ce8 100644
--- a/server/package.json
+++ b/server/package.json
@@ -26,6 +26,7 @@
     "argon2": "^0.29.1",
     "express": "^4.18.2",
     "express-async-handler": "^1.2.0",
+    "helmet": "^6.0.0",
     "jose": "^4.10.0",
     "loglevel": "^1.8.0",
     "reflect-metadata": "^0.1.13",