POST many-to-many

@auth_bp.route('/organization/<int:org_id>/add-user/', methods=['POST'])
def organization_user_add(org_id):
    user = g.user
    org = db.session.query(Organization).filter(Organization.id == org_id)
    user.organizations.append(org.first())
    db.session.add(user)
    db.session.commit()
    return jsonify({}), 201