Constructor: use token authentication to read secrets from a Vault path

        See https://www.vaultproject.io/docs/auth/token.html

        Args:
            url: Vault url
            path: Vault path where secrets are stored
            vault_token: token (must have access to vault path)

def from_token(cls, url, path, token):
        """Constructor: use token authentication to read secrets from a Vault path

        See https://www.vaultproject.io/docs/auth/token.html

        Args:
            url: Vault url
            path: Vault path where secrets are stored
            vault_token: token (must have access to vault path)
        """
        source_dict = cls._fetch_secrets(url, path, token)
        return cls(source_dict, url, path, token)