Generate private key and certificate for https

def generate_certificate_pure_python(common_name, size=DEFAULT_KEY_SIZE,
                                        digest=DEFAULT_DIGEST):
    '''
        Generate private key and certificate for https
    '''
    private_key = OpenSSL.crypto.PKey()
    private_key.generate_key(TYPE_RSA, size)

    request = OpenSSL.crypto.X509Req()
    subject = request.get_subject()
    setattr(subject, 'CN', common_name)
    request.set_pubkey(private_key)
    request.sign(private_key, digest)

    certificate = OpenSSL.crypto.X509()
    certificate.set_serial_number(0)
    certificate.gmtime_adj_notBefore(0)
    certificate.gmtime_adj_notAfter(60 * 60 * 24 * 365 * 5)
    certificate.set_issuer(request.get_subject())
    certificate.set_subject(request.get_subject())
    certificate.set_pubkey(request.get_pubkey())
    certificate.sign(private_key, digest)

    private_key_path = '{}/{}.key'.format(CERTIFICATES_PATH, common_name)
    if not os.path.isfile(private_key_path):
        print 'Write {}'.format(private_key_path)
        with open(private_key_path, 'w+') as private_key_file:
            private_key_file.write(
                OpenSSL.crypto.dump_privatekey(FILETYPE_PEM,
                                               private_key).decode('utf-8')
            )
        helpers.file_rights(private_key_path, mode=0400, uid=0, gid=0)
    else:
        print 'Already exist: {}'.format(private_key_path)

    certificate_path = '{}/{}.crt'.format(CERTIFICATES_PATH, common_name)
    if not os.path.isfile(certificate_path):
        print 'Write {}'.format(certificate_path)
        with open(certificate_path, 'w+') as certificate_file:
            certificate_file.write(
                OpenSSL.crypto.dump_certificate(FILETYPE_PEM,
                                                certificate).decode('utf-8')
            )
        helpers.file_rights(certificate_path, mode=0444, uid=0, gid=0)
    else:
        print 'Already exist: {}'.format(certificate_path)

    clean_links()
    make_links(common_name)