import org.bouncycastle.openssl.PEMWriter;
import org.bouncycastle.operator.ContentSigner;
import org.bouncycastle.pkcs.PKCS10CertificationRequest;
import org.bouncycastle.pkcs.PKCS10CertificationRequestBuilder;
import org.bouncycastle.pkcs.jcajce.JcaPKCS10CertificationRequestBuilder;
import org.bouncycastle.util.io.pem.PemObject;
import sg.sleek.pdf.signing.GoogleKMSContentSigner;

/*(imports)*/

public class GenerateCSR {

   private static PublicKey getPublicKey() throws IOException, NoSuchAlgorithmException, InvalidKeySpecException {
       File file = new File("<path to public file>");
       byte[] byteKey = Files.readAllBytes(file.toPath());

       X509EncodedKeySpec X509publicKey = new X509EncodedKeySpec(byteKey);
       KeyFactory kf = KeyFactory.getInstance("RSA");

       return kf.generatePublic(X509publicKey);
   }

   public static void main(String[] args) throws IOException,InvalidKeySpecException, NoSuchAlgorithmException {
       PKCS10CertificationRequestBuilder p10Builder = new JcaPKCS10CertificationRequestBuilder(
               new X500Principal("CN=Sleek, O=Sleek Tech (Pte. Ltd.), OU=, C=SG, L=Singapore"), getPublicKey());

       ContentSigner signer = new GoogleKMSContentSigner();
       PKCS10CertificationRequest csr = p10Builder.build(signer);

       PemObject pemObject = new PemObject("CERTIFICATE REQUEST", csr.getEncoded());
       StringWriter csrString = new StringWriter();
       PEMWriter pemWriter = new PEMWriter(csrString);
       pemWriter.writeObject(pemObject);
       pemWriter.close();
       csrString.close();

       //Certificate request will be printed into STDOUT
       System.out.println(csrString);
   }
}