First you must generate a certificate. To do so, go to resources/pl/edu/agh/dp/oauth2server. Then edit ssl_config to include server IP (last line of the file - replace A.B.C.D with your local IP). Next, run generate_key.sh to generate a certificate. Finally, make your system trust your generated certificate (Windows).
If you use Postman, you can alternatively add certificate (cert.pem) only in postman (File -> Settings -> Certificates -> CA Certificates).