Java 如何将AttCertValidityPeriod添加到PKCS10CertificationRequest CSR并从CSR检索回它？

我正在实现一个示例代码来生成CSR并用证书对其进行签名。我需要在生成CSR时将有效期添加为属性，并在签名部分中读取该属性以根据该属性进行签名。如何将该属性添加到CSR并检索回来

我用于生成CSR的当前代码：

 public static PKCS10CertificationRequest generateCSR(KeyPair keyPair, String o, String cn) throws IOException,
            OperatorCreationException {
        X500Name principal = new X500NameBuilder()
                .addRDN(BCStyle.O, o)
                .addRDN(BCStyle.CN, cn)
                .build();

        ContentSigner signer = new JCESigner (keyPair.getPrivate(),DEFAULT_SIGNATURE_ALGORITHM);

        PKCS10CertificationRequestBuilder csrBuilder = new JcaPKCS10CertificationRequestBuilder(principal, keyPair.getPublic());
        ExtensionsGenerator extensionsGenerator = new ExtensionsGenerator();
        extensionsGenerator.addExtension(Extension.basicConstraints, true,
                new BasicConstraints(true));

        csrBuilder.addAttribute(PKCSObjectIdentifiers.pkcs_9_at_extensionRequest,
                extensionsGenerator.generate());

        PKCS10CertificationRequest csr = csrBuilder.build(signer);

        return csr;
    }

}