Generate JWT token for Apple iOS inApp subscription using p8 private key file

JWTUtil.java

import com.nimbusds.jose.JWSAlgorithm;
import com.nimbusds.jose.JWSHeader;
import com.nimbusds.jose.JWSSigner;
import com.nimbusds.jose.crypto.ECDSASigner;
import com.nimbusds.jwt.JWTClaimsSet;
import com.nimbusds.jwt.SignedJWT;

public class JWTUtil {

    public static String generateJWTForiOS() {
        String token = "";
        try {
            String kid = "";
            String iss = "";
            String aud = "appstoreconnect-v1";
            String bid = "";

            // current date as Date object
            Date now = new Date();
            // current date plus 20 minutes as Date object
            Date exp = new Date(now.getTime() + 20 * 60 * 1000);

            PrivateKey key = loadiOSPrivateKey();

            JWTClaimsSet claimsSet = new JWTClaimsSet
                    .Builder()
                    .audience(aud)
                    .expirationTime(exp)
                    .issueTime(now)
                    .issuer(iss)
                    .claim("bid", bid)
                    .build();

            JWSHeader header = new JWSHeader
                    .Builder(JWSAlgorithm.ES256)
                    .keyID(kid)
                    .build();

            SignedJWT signedJWT = new SignedJWT(header, claimsSet);
            JWSSigner signer = new ECDSASigner((java.security.interfaces.ECPrivateKey) key);
            signedJWT.sign(signer);
            token = signedJWT.serialize();
            System.out.println(token);

        } catch (Exception e) {
            e.printStackTrace();
        }
        return token;
    }
}