async getIdentityTokenForMemberFromSession(req, res) {
        const transientId = this._getSessionCookies(req, res);
        const token = await this._getMemberIdentityToken(transientId);
        if (!token) {
            await this.deleteSession(req, res);
            throw new BadRequestError({
                message: 'Invalid session, could not get identity token'
            });
        }
        return token;
    }
@method getIdentityTokenForMemberFromSession

@param {Request} req
@param {Response} res

@returns {Promise<JWT>} identity token