code: def _get_subject_public_key(cert):
          
          public_key = cert.get_pubkey()
          cryptographic_key = public_key.to_cryptography_key()
          subject_public_key = cryptographic_key.public_bytes(Encoding.DER,
                                                              PublicFormat.PKCS1)
          return subject_public_key
docs: Returns the SubjectPublicKey asn.1 field of the SubjectPublicKeyInfo
          field of the server's certificate. This is used in the server
          verification steps to thwart MitM attacks.
  
          :param cert: X509 certificate from pyOpenSSL .get_peer_certificate()
          :return: byte string of the asn.1 DER encoded SubjectPublicKey field