PR,
you must follow the Admin guide to setup trusted auth's choosing the appropriate user retrieval methods available. you may post issues you come across while performing the configuration
check following kb's if you need 'query_string' or 'http_header' method:
1593628 - Setting up Trusted Authentication in BI4 for BIlaunchPad and Opendocument using QUERY_STRING
1603002 - Setting up Trusted Authentication in BI4 for BIlaunchPad and Opendocument using HTTP_HEADER
NOTE: IF, you users login to the portal using the same user/pass that they have used to login to their Windows machines, you can also setup vintela (Windows AD) SSO since your CMS is on Windows. no need for trusted auth here).
-Nikhil Nair