Web Hacking

Goal  : Finding a backup file on servername:1338
When i connect to the website a login page appears with a register option.
I tried to wget -r command to get files i got that login.php verifies credentials on /php/auth1.php
i tried to wget the file i downloaded it but it contains nothing.
Is there any idea how i can check for the backup file ( i tried to find index.php index.php.bak and something similar)
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