If you are starting from the Content Management System (doceboCms) the file
docebo/doceboCms/lib/lib.preoperation.php
contains two functions of interest: cms_do_login() and cmsJumpBack().
At the end of cms_do_login() there is a call to cmsJumpBack() which
calls jumpTo($backurl) to perform a website redirect using the Location
header. You could change this to a jumpTo('page_of_interest.php')
if you know exactly how to call the page_of_interest.
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If you are starting from the Learning Course Management System (doceboLms) the file
docebo/docebLms/lib/lib.preoperation.php
contains a line 197:
jumpTo('index.php?modname='.$GLOBALS['modname'].'&op='.$GLOBALS['op']);
where a structurally similar redirect takes place.