System for authenticating a user comprising: a user terminal; and an authentication apparatus; the system further comprises an information processing apparatus, wherein the information processing apparatus, the user terminal and the authentication apparatus are connected to each other; wherein the information processing apparatus is configured to provide the user terminal access to an external apparatus (40, 50) via the information processing apparatus; wherein said information processing apparatus is configured to use a function (45, 55) of the external apparatus (40, 50) using certificate information from the authentication apparatus for authenticating the user; the information processing apparatus comprises: a receiving unit configured to receive authentication information (613, 614) received from the user terminal, wherein the authentication information (613, 614) is inputted by the user at the user terminal, wherein the authentication information is used to cause the authentication apparatus to authenticate the user; a first acquiring unit (17, 172) configured to send the authentication information (613, 614) to the authentication apparatus as a first request, to obtain first certification information (622; 633) which indicates that the user has been authenticated, and to acquire the first certification information (622; 633) being a master ticket (622; 633) from the authentication apparatus as a response to the first request; and a second acquiring unit (17, 173) configured to send the first certification information (622; 633) to the authentication apparatus, as a second request, to obtain a second certification information, and to acquire the second certification information being an authentication ticket needed to use the function (45, 55) of the external apparatus (40, 50). a user terminal; and an authentication apparatus; the system further comprises an information processing apparatus, wherein the information processing apparatus, the user terminal and the authentication apparatus are connected to each other; wherein the information processing apparatus is configured to provide the user terminal access to an external apparatus (40, 50) via the information processing apparatus; wherein said information processing apparatus is configured to use a function (45, 55) of the external apparatus (40, 50) using certificate information from the authentication apparatus for authenticating the user; the information processing apparatus comprises: a receiving unit configured to receive authentication information (613, 614) received from the user terminal, wherein the authentication information (613, 614) is inputted by the user at the user terminal, wherein the authentication information is used to cause the authentication apparatus to authenticate the user; a first acquiring unit (17, 172) configured to send the authentication information (613, 614) to the authentication apparatus as a first request, to obtain first certification information (622; 633) which indicates that the user has been authenticated, and to acquire the first certification information (622; 633) being a master ticket (622; 633) from the authentication apparatus as a response to the first request; and a second acquiring unit (17, 173) configured to send the first certification information (622; 633) to the authentication apparatus, as a second request, to obtain a second certification information, and to acquire the second certification information being an authentication ticket needed to use the function (45, 55) of the external apparatus (40, 50). a receiving unit configured to receive authentication information (613, 614) received from the user terminal, wherein the authentication information (613, 614) is inputted by the user at the user terminal, wherein the authentication information is used to cause the authentication apparatus to authenticate the user; a first acquiring unit (17, 172) configured to send the authentication information (613, 614) to the authentication apparatus as a first request, to obtain first certification information (622; 633) which indicates that the user has been authenticated, and to acquire the first certification information (622; 633) being a master ticket (622; 633) from the authentication apparatus as a response to the first request; and a second acquiring unit (17, 173) configured to send the first certification information (622; 633) to the authentication apparatus, as a second request, to obtain a second certification information, and to acquire the second certification information being an authentication ticket needed to use the function (45, 55) of the external apparatus (40, 50).