We have just upgraded from Xerte 3.0 to 3.4. The use of Shibboleth seems to have become somewhat easier in that all we did was:
1) replace the 'library/Xerte/Authentication/Saml2.php' file with our 'Shibboleth.php' file - but keep the name the same (i.e. 'Saml2.php').
This then allows you to select the authentication method as the already provided 'Saml2'. You don't need to create a new 'Shibboleth' log in method, and by overwriting the existing Saml2 method also means that we have to modify less files.
2) We modified the 'website_code/php/login_library.php' so that for 'Saml2' no username/password boxes were shown. Clicking on the Login button just took you to the shibboleth login URL, and provided a return location as well. (This is the same as we did before, just a bit tidier in the 3.4 version.)
That was really all there was to it. As before, the main part is writing your own 'Shibboleth.php' (or rather 'Saml2.php') file to suit your own Shibboleth set up.
John.