Specify SP target URL to previous page (referer)

[Jehan Procaccia]

Hello

from 
https://wiki.shibboleth.net/confluence/display/SHIB2/NativeSPSessionCreationParameters
I understand that the target parameter is an absolute URL
is it possible to have it set to a  the variable previous page (referer) 
the request originated from ?

for example while browsing anonymously (not conected) our library 
application shows us a book
https://catalogue.mines-telecom.fr/cgi-bin/koha/opac-detail.pl?biblionumber=84779
if I want to reserve it, I am redirected to an intermediary page with a 
shib login button pointing to a hard coded target that brings me back to 
my user profile (here opac-user.pl)
https://catalogue.mines-telecom.fr/Shibboleth.sso/Login?providerId=https://idp.tem-tsp.eu/idp/shibboleth&target=https://catalogue.mines-telecom.fr/cgi-bin/koha/opac-user.pl
that's ok for usual connexions,
but in the context of having   anonymously preselected a book, I would 
like to be back to that context, that is the "referer" page .
How can I set dynamically the target to the previous/referer page ? is 
it possible to set the target as a "variable" pointing to the "referer" ?

Thanks .