A method for authenticating a terminal by a gateway of an internal network protected by an entity providing secure access. The authentication method according to the invention comprises: after receiving a request originating from a web browser of the terminal comprising a user identifier (ID-U), obtaining authentication data (PWD-U) associated with this identifier stored in a database of the internal network; configuring a proxy server authorising, at the entity providing secure access, access to the internal network to a predefined set of connection parameters; generating a first application from connection parameters from this set, protected by means of at least one predefined portion of the authentication data and capable of establishing, when it is executed by the web browser, a connection between the terminal and the proxy server using said parameters, in response to the provision of said at least one portion of the authentication data; and transmitting the first application to the web browser of the terminal.