<p>This paper proposes a mediated semi-quantum identity authentication (MSQIA) protocol that enables secure authentication between classical users and a quantum cloud server using single-photon qubits. Unlike traditional protocols that require entanglement or full quantum capabilities, our approach accommodates classical participants limited to Z-basis measurements and reflections. By integrating a polarization mapping scheme and pre-shared secrets, the protocol provides robust defense against impersonation, intercept-resend, measure-resend, entanglement, and Trojan horse attacks. We further extend the model to a multiparty setting and discuss issues of scalability, synchronization, and polarization precision. A comparative analysis of existing lightweight semi-quantum authentication protocols demonstrates the efficiency and practical viability of our approach.</p>