async decodeToken(token) {
        await this._keyStoreReady;

        const result = jwt.verify(token, this._publicKey, {
            algorithms: ['RS512'],
            issuer: this._issuer
        });

        if (typeof result === 'string') {
            return {sub: result};
        }

        return result;
    }
@param {string} token
@returns {Promise<jwt.JwtPayload>}