Recently have been working on the issue when the users on iOS 9 and 10 were not able to complete the authentication from outside of corporate network (via AD FS Proxy). The users were getting the error – “There was a problem accessing the site. Try to browse to the site again. Reference number: XXX”.
The same users from iOS 11 had no issues signing in via the same AD FS farm.
The users were the members of 150-200 on premises AD security groups.
It took me some time to go over basic troubleshooting and making sure the AD FS servers have all needed patches installed – https://docs.microsoft.com/en-us/windows-server/identity/ad-fs/deployment/updates-for-active-directory-federation-services-ad-fs, but the issue persisted.
Turned out to be a known issue, when the older Safari versions have cookies size limitation.
Looking at the captured Fiddler trace we saw the AD FS was issuing 5 MSISAuth cookies (total size around 9 Kb) and when Safari was redirected to ADFS to get the access token, only 4 MSISAuth cookies were posted to ADFS (around 8 Kb). In this case Safari was dropping the cookies.
In order to work around this issue, the customer decided to do not pass all 200 security groups in the claims.
In order to achieve this, the default “Pass through all Group SID claims” was replaced with following claim rule since the customer was using these groups in his Authorization claim rules: