For physical-layer authentication, the authentication tags are often sent concurrently with messages without much bandwidth expansion. In this paper, we present a channel coding approach for physical-layer authentication. The generation of authentication tags can be formulated as an encoding process for an ensemble of codes, where the shared key between Alice and Bob is considered as the input and the message is used to specify a code from the ensemble of codes. Then, we show that the security of physical-layer authentication schemes can be analyzed through decoding and physical-layer authentication schemes can potentially achieve both information-theoretic and computational securities.