asn1: Support integration with x509.Certificate, x509.CertificateSigningRequest, x509.CertificateRevocationList

[loewexy]

While working with the new asn1 library to implement the CMS format i missed one integration between the asn1 module and the x509.* classes. It would be nice if something like the following could work.

@asn1.sequence
class Test:
  cert: x509.Certificate

To include the Certificate, CSR or CRL objects that cryptography already has in the structure, without complexity. Currently the only option would be to do someting like:

_cert = load_pem_certificate(...)

@asn1.sequence
class Test:
  cert: asn1.TLV

# Create object
obj = Test(cert=asn1.TLV(
  _cert.public_bytes(encoding=Encoding.DER)
))

# Get cert from object
_cert_from_obj = load_der_certificate(obj.cert)

And i am not even sure if this would work. But nevertheless it is not a nice solution.

[alex]

This is an interesting idea, but I'm not sure there's an obvious way to make it actually work.

[loewexy]

It should be possible to use the TLV workaround in the lib directly. So when a type annotation is Certificate, CSR or CRL the code for serializin could just call .public_bytes on the object and wrap them in a asn1.TLV object. And when parsing could consider it as a TLV value, and use the load_der_certificate functions.

However I fear this is out of my expertise, since i do not understand the complete ASN1 implementation and also have no experience in Rust.