Authentication method, application client and gateway device

The invention discloses an authentication method. An APP client builds data connection with a SDK (Software Development Kit) platform in a condition in which the SDK platform passes the first authentication. The method also comprises steps: the APP client receives secondary authentication information transmitted by the SDK platform, wherein the secondary authentication information at least comprises an encryption algorithm, a key, and an APP identity; based on the secondary authentication information, a unified payment traffic message is generated, wherein a field value corresponding to the authentication field of the unified payment traffic message comprises ciphertext information obtained at least based on a message feature value of the unified payment traffic message, the encryption algorithm and the key, and plaintext information obtained at least based on the APP identity; and the unified payment traffic message is transmitted to a unified payment gateway for traffic authentication. The invention also di