wget
--user-agent="Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0)
Gecko/20100101 Firefox/45.0"
--keep-session-cookies
--save-cookies cookies.txt
--post-data "login_username=MyUserName&login_password=*******"
--header="Host: somewebsite.com"
--header="Referer: http://somewebsite.com/files/dl.php?t=2157716"
http://somewebsite.com/login.php

wget
--user-agent="Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0)
Gecko/20100101 Firefox/45.0"
--load-cookies cookies.txt
--header="Host: somewebsite.com"
--header="Referer: http://somewebsite.com/files/dl.php?t=2157716"
http://somewebsite.com/files/dl.php?t=2157716