Creación de un token web JSON (JWT)

public String getJWTToken()
    {
            Security.addProvider(new BouncyCastleProvider());
            RSAPrivateKey privateKey = null;
            GetServiceCredentials getCredentials = new GetServiceCredentials();
            try
            {

                long now = System.currentTimeMillis();
                Long expirationTime = now + TimeUnit.MINUTES.toMillis(5);
                // get the private key string from the service credentials
                String privateKeyString = getCredentials.getPRIVATE_KEY();
                //The JWT signature algorithm we use to sign the token
                SignatureAlgorithm sa = SignatureAlgorithm.RS256;


                Reader targetReader = new StringReader(privateKeyString);
                // PEMParser removes the unnecessary headers and decodes the underlying Base64 PEM data into a binary format.
                PEMParser pemParser = new PEMParser(targetReader);
                // tores the result generated by the pEMParser
                Object object = pemParser.readObject();
                JcaPEMKeyConverter converter = new JcaPEMKeyConverter().setProvider("BC");
                KeyPair kp = converter.getKeyPair((PEMKeyPair) object);
                privateKey = (RSAPrivateKey) kp.getPrivate();

              //Let's set the JWT Claims

                Map < String, Object > jwtClaims = new HashMap < String, Object > ();
                jwtClaims.put("iss", getCredentials.getORG_ID());
                jwtClaims.put("sub", getCredentials.getTECH_ACCT());
                jwtClaims.put("exp", expirationTime);
                jwtClaims.put("aud", "https://" + getCredentials.getIMS_ENDPOINT() + "/c/" + getCredentials.getCLIENT_ID());
                String metascopes[] = new String[] { getCredentials.getMETASCOPE_ID() };

                for (String metascope: metascopes)
                {
                            jwtClaims.put("https://" + getCredentials.getIMS_ENDPOINT() + "/s/" + metascope, java.lang.Boolean.TRUE);
                }


                // Create the final JWT token
                String jwtToken = Jwts.builder().setClaims(jwtClaims).signWith(sa, privateKey).compact();
                    System.out.println("Got JWT Token " + jwtToken);
                    pemParser.close();
                return jwtToken;

            } catch (IOException e) {

                    System.out.println("The error is " + e.getMessage());
            }
            return null;

    }