docs: def issuer(self, value):
          """
          An asn1crypto.x509.Certificate or oscrypto.asymmetric.Certificate object
          of the issuer.
          """
  
          is_oscrypto = isinstance(value, asymmetric.Certificate)
          if not is_oscrypto and not isinstance(value, x509.Certificate):
              raise TypeError(_pretty_message(
                  '''
                  issuer must be an instance of asn1crypto.x509.Certificate or
                  oscrypto.asymmetric.Certificate, not %s
                  ''',
                  _type_name(value)
              ))
  
          if is_oscrypto:
              value = value.asn1
  
          self._issuer = value