It looks like the right place to get current RPMs of Shibboleth is https://shibboleth.net/downloads/service-provider/latest/RPMS/. You can choose your OS on that page.
Note that the instructions you quote are very old, so there's no guarantee that they will work with the current version of WeBWorK (2.17).
Note that due to significant changes in the upcoming version of WeBWorK (2.18 - to be released this Summer) which migrates WeBWorK from mod-perl to mojolicious, the current implementation of Shibboleth will not be compatible. Work will need to be done to develop a Shibboleth implementation that works with the new architecture.