when you say login, do you mean logon to the WiFi Network for Internet Access or Login to the Routers Admin Page to change Settings etc.
These will probably be two different User and Passwords access unless someone has changed them.
The First will be WiFi access, which will be WiFi Name followed by the WiFi Password, sometimes referred to a WiFi Key on the Box or Router etc.
The second, will be Admin User and Admin Password in order to access the Admin Page for Settings etc, you need to Access the WiFi part first before you can access the Admin part if your doing this over WiFi.
So, WiFi and Key / Password to logon to the Routers WiFi for Internet, then should you need to, login to Admin with User and Password both different and all info should be on the Box, Router or a Card etc
