How to use the bless.ssh.public_keys.ssh_public_key.SSHPublicKeyType.RSA function in bless

def test_valid_key_valid_password():
    ca = get_ssh_certificate_authority(RSA_CA_PRIVATE_KEY, RSA_CA_PRIVATE_KEY_PASSWORD)
    assert isinstance(ca, RSACertificateAuthority)
    assert SSHPublicKeyType.RSA == ca.public_key_type
    assert 65537 == ca.e
    assert ca.get_signature_key() == RSA_CA_SSH_PUBLIC_KEY

def __init__(self, ssh_public_key):
        """
        Extracts the useful RSA Public Key information from an SSH Public Key file.
        :param ssh_public_key: SSH Public Key file contents. (i.e. 'ssh-rsa AAAAB3NzaC1yc2E..').
        """
        super(RSAPublicKey, self).__init__()

        self.type = SSHPublicKeyType.RSA

        split_ssh_public_key = ssh_public_key.split(' ')
        split_key_len = len(split_ssh_public_key)

        # is there a key comment at the end?
        if split_key_len > 2:
            self.key_comment = ' '.join(split_ssh_public_key[2:])
        else:
            self.key_comment = ''

        public_key = serialization.load_ssh_public_key(ssh_public_key.encode('ascii'), default_backend())
        ca_pub_numbers = public_key.public_numbers()
        if not isinstance(ca_pub_numbers, RSAPublicNumbers):
            raise TypeError("Public Key is not the correct type or format")

        self.key_size = public_key.key_size

def get_ssh_public_key(ssh_public_key):
    """
    Returns the proper SSHPublicKey instance based off of the SSH Public Key file.
    :param ssh_public_key: SSH Public Key file contents. (i.e. 'ssh-XXX AAAA....').
    :return: An SSHPublicKey instance.
    """
    if ssh_public_key.startswith(SSHPublicKeyType.RSA):
        rsa_public_key = RSAPublicKey(ssh_public_key)
        rsa_public_key.validate_for_signing()
        return rsa_public_key
    elif ssh_public_key.startswith(SSHPublicKeyType.ED25519):
        ed25519_public_key = ED25519PublicKey(ssh_public_key)
        return ed25519_public_key
    else:
        raise TypeError("Unsupported Public Key Type")

def __init__(self, pem_private_key, private_key_password=None):
        """
        RSA Certificate Authority used to sign certificates.
        :param pem_private_key: PEM formatted RSA Private Key.  It should be encrypted with a
        password, but that is not required.
        :param private_key_password: Password to decrypt the PEM RSA Private Key, if it is
        encrypted.  Which it should be.
        """
        super(SSHCertificateAuthority, self).__init__()
        self.public_key_type = SSHPublicKeyType.RSA

        self.private_key = load_pem_private_key(pem_private_key,
                                                private_key_password,
                                                default_backend())

        ca_pub_numbers = self.private_key.public_key().public_numbers()

        self.e = ca_pub_numbers.e
        self.n = ca_pub_numbers.n

def get_ssh_certificate_builder(ca, cert_type, public_key_to_sign):
    """
    Returns the proper SSHCertificateBuilder instance for the type of public key to be signed.
    :param ca: The SSHCertificateAuthority that will sign the certificate.  The
    SSHCertificateAuthority type does not need to be the same type as the SSHCertificateBuilder.
    :param cert_type: The SSHCertificateType.  Is this a User or Host certificate?
    :param public_key_to_sign: The SSHPublicKey to issue a certificate for.
    :return: An SSHCertificateBuilder instance.
    """
    # Determine the type of public key we have, to decide the right cert type
    ssh_public_key = get_ssh_public_key(public_key_to_sign)

    if ssh_public_key.type is SSHPublicKeyType.RSA:
        return RSACertificateBuilder(ca, cert_type, ssh_public_key)
    elif ssh_public_key.type is SSHPublicKeyType.ED25519:
        return ED25519CertificateBuilder(ca, cert_type, ssh_public_key)
    else:
        raise TypeError("Unsupported Public Key Type")