The quasi(now-supported unofficial) Mac installation mechanism is the MacPorts system. MacPorts is a software package similar to the BSD ports facility that uses descriptors called Portfiles to download and install open source packages, either from pre-built cached binaries or from source.
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Of course, building Shibboleth from source is also possible (and tends to be more reliable but is much more work).
Install using MacPorts
Build from Source
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