Apple requests to its APNS must use JWT (JSON Web Token) signed using a Elliptic Curve Digital Signature Algorithm aka ECSDA using a p-256 curve and a SHA256 hash. How can you sign with such params in openssl?
openssl ecparam -list_curves
shows:
secp256k1 : SECG curve over a 256 bit prime field
prime256v1: X9.62/SECG curve over a 256 bit prime field