There are 3 repositories under single-packet-authorization topic.
OpenSPA - An open and extensible Single Packet Authorization (SPA) protocol
Layer 4 Single Packet Authentication utilizing Netfilter Queue and libnetfilter.
Securing the Software-Defined Perimeter framework with automated security configuration deployment systems
nfqueue/ipset-based port knocking using JWT (JSON Web Token) as SPA (Single Packet Authorization)
Unofficial OpenSPA Dockerfiles