An embodiment of the invention may include a method, computer program product and system for secure authentication within a communication protocol session. The embodiment may include retrieving, by a client computer of the TLS session, a challenge string associated with the TLS session. The embodiment may include generating, by the client computer, a first digest based on the challenge string and authentication information of a user of the client computer. The embodiment may include sending, by the client computer, the first digest to a server of the TLS session. The retrieving, generating and sending, by the client computer, are carried out after the TLS session has been established between the client computer and the server.