The invention relates to a method for authentication of a person previously known by a server to own a telephone having a unique identifier and to possess an access code, which method involves: the server sending (53) an identification code to a terminal on request by the latter via a first network; transferring (57) the identification code to the telephone; the server receiving (59), from the telephone via a second network, the identification code in association with the unique identifier; the server (61) generating a single-use authentication token and sending (63) the latter to the telephone; returning (64) the token to the server; and, in parallel: acquiring (67) via the terminal the access code input by the person; and sending (69) said access code to the server; authentication (71) of the person is obtained by the server if the identification code, the unique identifier, the authentication token and the access code correspond.