JWT signing with public and private key - spring

Question

I have written this portion of code to create a JWT.
public String createJWT() throws JoseException {
RsaJsonWebKey rsaJsonWebKey = RsaJwkGenerator.generateJwk(2048);
// Give the JWK a Key ID (kid), which is just the polite thing to do
rsaJsonWebKey.setKeyId(keyId);
// Create the Claims, which will be the content of the JWT
JwtClaims claims = new JwtClaims();
claims.setIssuer(issuer);
claims.setExpirationTimeMinutesInTheFuture(60);
claims.setJwtId(keyId);
claims.setIssuedAtToNow();
claims.setNotBeforeMinutesInThePast(2);
claims.setSubject(subject);
// We create a JsonWebSignature object.
JsonWebSignature jws = new JsonWebSignature();
// The payload of the JWS is JSON content of the JWT Claims
jws.setPayload(claims.toJson());
//The header of the JWS
jws.setHeader("typ", "JWT");
// The JWT is signed using the private key
jws.setKey(rsaJsonWebKey.getPrivateKey());
jws.setKeyIdHeaderValue(rsaJsonWebKey.getKeyId());
// Set the signature algorithm on the JWT/JWS that will integrity protect the claims
jws.setAlgorithmHeaderValue(AlgorithmIdentifiers.RSA_USING_SHA256);
// Sign the JWS and produce the compact serialization or the complete JWT/JWS
// representation, which is a string consisting of three dot ('.') separated
// base64url-encoded parts in the form Header.Payload.Signature
String jwt = jws.getCompactSerialization();
System.out.println("JWT: " + jwt);
return jwt;
}
But I don't understand which private key is it retrieving? How can I customize this code to send my own public and private key stored in local JKS??
Thanks in advancee!!

Answer 1

Try to use the following to load your own keystore:
try (InputStream is = new FileInputStream(new File("path to keystore"))) {
KeyStore keyStore = KeyStore.getInstance(ksType);
keyStore.load(is, password);
final Enumeration<String> aliases = keyStore.aliases();
final String alias = aliases.nextElement(); // assuming only one entry
final Entry entry = keyStore.getEntry(alias, password);
if (entry instanceof PrivateKeyEntry) {
PrivateKeyEntry pke = (PrivateKeyEntry) entry;
PrivateKey privateKey = pke .getPrivateKey();
// and here you may return the PrivateKey
}
} catch (Exception e) {
...
}
Disclaimer : I did not test the code, but it should work.