Maybe your IdP expects SOAP over HTTP but your SP won't. Perhaps the SP insists on encrypting AuthnRequests. God help you if one side wants to do URL encoding and DEFLATE.
I've made my life easier by refusing to ask/answer questions around SSO and instead insisting on talking about "ADFS login". We still do SAML, but at least there's a baseline implementation that I can plan for.
I implemented a SAML IdP [0] in MUCH less time than it took to configure Shibboleth. The specification for SAML is pretty easy to comprehend.
The implementation is really an experiment, but the configuration and usability is significantly better. Improving the implementation doesn't affect this. In some closed-source forks I've written a production version that's been in use for several years.
[0] https://github.com/rkeene/saml-idp/blob/master/lib/saml/saml...
I love IT and programming, but I knew if I made a life long career of it, I'd grow to hate it.
I really like doing IT related things in my own way. I'd always want to do things to best practices and not just get the job done as I was told.
I made the switch out of IT to another field. Configuring a Shibboleth IdP was probably the hardest thing I ever had to do in my IT career, it really pushed my capabilities. SLO wasn't the only hard thing, the whole thing was immensely challenging and every time I'd restart Jetty I'd be holding my breath hoping it would come up again.