Hi Sergio,
Unfortunately we at Artefactual can offer only very limited general suggestions with this. The CENDARI Shibboleth plugin was developed against an older version of AtoM, and has not been incorporated into a public release (as similar work has been in Archivematica), nor does it appear to have been maintained and tested against more recent versions of AtoM. I have heard reports in this forum of users getting it to work with AtoM 2.4, but so far no one's reported implementing it against AtoM 2.5 - though it may have happened!
Hopefully others on the forum who have worked with this plugin can provide further guidance.
Best of luck, and let us know how it goes!