'`cert_string` is a certificate in the form you get from running a
.crt through \'openssl x509 -in CERT.cert -text\''

def __init__(self, cert_string):

    self.cert_string = cert_string
    self.serial = None
    self.subject = None
    self.extensions = []
    self.not_after = None
    self._parse_cert()
