Produce an object suitable for an ASN1OutputStream.
AttributeCertificate ::= SEQUENCE {
acinfo AttributeCertificateInfo,
signatureAlgorithm AlgorithmIdentifier,
signatureValue BIT STRING
}
ASN1EncodableVector v = new ASN1EncodableVector();
v.add(acinfo);
v.add(signatureAlgorithm);
v.add(signatureValue);
return new DERSequence(v);