Abstract: The invention relates to a method for authenticating a user (1) on the basis of a mobile terminal of the cellular phone type (2), in which said user (1) views through a browser a portal for accessing a service hosted on a server (4); said user (1) requests his authentication through the browser via said portal; said portal initiates a pre-session in such a way as to display, through said browser, temporary access data (5) independent from said user (1); said user (1) inputs into his telephone (2) the data viewed; said telephone (2) automatically dispatches a request (6) to said server (4), including at least one authentication certificate (7) specific to the user (1) and said viewed data (5); said request (6) is encrypted with the aid of the public key of a certificate (8) of said server (4) and, in the event of authentication of the user (1), access to the service is authorized through a secure session in the browser.