code: public BcX509v3TBSCertificateBuilder setExtensions(CertifiedPublicKey issuer, PublicKeyParameters subject,
          X509Extensions extensions1, X509Extensions extensions2) throws IOException
      {
          DefaultX509ExtensionBuilder extBuilder = new DefaultX509ExtensionBuilder();
  
          extBuilder.addAuthorityKeyIdentifier(issuer)
              .addSubjectKeyIdentifier(subject)
              .addExtensions(extensions1)
              .addExtensions(extensions2);
  
          if (!extBuilder.isEmpty())
          {
              this.tbsGen.setExtensions(((BcX509Extensions) extBuilder.build()).getExtensions());
          }
          return this;
      }
docs: Set the extensions of a v3 certificate.
  
  @param issuer the issuer certified public key to compute the Authority Key Identifier, or null for none.
  @param subject the subject certified public key parameters to compute the Subject Key Identifier, or null for
  none.
  @param extensions1 the common extensions set.
  @param extensions2 the subject extensions set.
  @return this builder to allow chaining.
  @throws IOException on encoding error.