code: public void verify() throws Exception {
  
          Map<String, ProxyPolicyHandler> handlers = null;
          if (proxyCertInfo != null) {
              String oid = proxyCertInfo.getProxyPolicy().getPolicyLanguage().getId();
              handlers = new HashMap<String,ProxyPolicyHandler>();
              handlers.put(oid, new ProxyPolicyHandler() {
                  public void validate(ProxyCertInfo proxyCertInfo,
                           CertPath certPath,
                           int index)
                  throws CertPathValidatorException {
                  // ignore policy - this is just for proxy init case
                  System.out.println("Proxy verify: Ignoring proxy policy");
                  if (debug) {
                      String policy =
                      new String(proxyCertInfo.getProxyPolicy().getPolicy());
                      System.out.println("Policy:");
                      System.out.println(policy);
                  }
                }
              });
          }
  
          KeyStore keyStore = Stores.getDefaultTrustStore();
          CertStore crlStore = Stores.getDefaultCRLStore();
          ResourceSigningPolicyStore sigPolStore = Stores.getDefaultSigningPolicyStore();
          X509ProxyCertPathParameters parameters = new X509ProxyCertPathParameters(keyStore, crlStore, sigPolStore, false, handlers);
          X509ProxyCertPathValidator validator = new X509ProxyCertPathValidator();
          validator.engineValidate(CertificateUtil.getCertPath(proxy.getCertificateChain()), parameters);
      }
docs: verifies the proxy credential