An authentication method is disclosed herein. The method includes: by a server, using a Trigger message nonce to generate a Trigger message, and sending the generated Trigger message to a client so that the client can extract the Trigger message nonce; after determining that the Trigger message nonce is valid, using the Trigger message nonce to generate a digest, and authenticating the Trigger message generated by using the Trigger message nonce; after the authentication succeeds, sending a session request to the server indicated by the Trigger message, where the session request carries a session ID. The corresponding system, server and client are disclosed herein. The present invention makes the authentication process more secure through the client and the server based on the DS or DM protocol.