인증서 변환하기openssl pkcs12 -in dev_apns_demo.p12 -out dev_apns_demo.pem -nodes -clcerts인증서 확인하기openssl s_client -connect gateway.sandbox.push.apple.com:2195 -cert dev_apns_demo.pem -key dev_apns_demo.pem으갸갹.