feat: add local admin authentication

app/auth/admin.py

@@ -0,0 +1,12 @@
+import hmac
+
+from fastapi import HTTPException, Request, status
+
+
+def password_matches(submitted: str, configured: str) -> bool:
+    return hmac.compare_digest(submitted.encode("utf-8"), configured.encode("utf-8"))
+
+
+def require_admin(request: Request) -> None:
+    if request.session.get("admin_authenticated") is not True:
+        raise HTTPException(status_code=status.HTTP_303_SEE_OTHER, headers={"Location": "/login"})