Cities of several classes in this state shall be empowered to regulate the use of sidewalks within their limits, and may in their discretion and under such terms and conditions as they may determine permit a use of the same by abutting owners, provided such use does not in their judgment unduly and unreasonably impair passage thereon, to and fro, by the public. Such permission shall not be considered as establishing a prescriptive right, and the right may be revoked at any time by the authorities of such cities.