A good friend of mine was experiencing an issue with accessing the online features of Halo 5, and from doing a bit of googling, it appears he’s not the only one.
The error he was getting was:
Error Authorizing user with Halo 5: Guardians services. You will be unable to access online modes.
We did manage to fix the issue however…
It turned out that Sky Shield (an ISP-based internet filter) was blocking connection to certain sites that Halo required access to.
He resolved it by disabling the Sky Shield, maybe not be the best idea in all circumstances, but according to what I’ve read, whitelisting “www.halowaypoint.com” will also fix the problem.
If you’re experiencing this I would recommend looking at whether you have any services filtering allowed sites. It’ll likely appear to be a Halo specific problem, with a slightly misleading error message, the cause wasn’t immediately clear!
Let me know if this has resolved your issue!