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Monday, October 21, 2019

AAD Connect and Pass Through Auth Possible Gotcha

Hello again everyone!

Been awhile!

I want to make a quick post about an issue I ran into out in the field in regards to AAD Connect, Pass-Thru Auth, and log on restrictions in local AD. 

**Spoiler Alert** Read your documentation thoroughly and you can avoid stupid mistakes like this one!

Lets start off with a brief explanation on what Pass-Thru Auth is. This method of auth/ssso is similar to ADFS. When you attempt to auth against O365/Azure AD it will send the request back on premise to an agent that is installed on a member server. 

There are certain requirements that this member server needs that we wont go into in this post, such as line of sight to a DC, multiple agents for HA, etc, etc.

Now onto what the issue was.

At a client we recently had a group of users, well maybe 'users' is not the correct word for it, nor is 'service accounts'. It was a handful of user objects in AD that the security team used to log into a very specific set of workflows on premise and into a couple services in the cloud. 

They just stopped authenticating one day. 

When trying to auth against a cloud service they would receive this error 'Service is currently unavailable, please contact support for further help'

When we looked at the sign in logs inside of Azure AD this is what we saw.



We tinkered with the idea that AAD Connect was not syncing the password so we took a look at the health monitor. Everything looked good but thats when I saw they were using Pass-Thru Auth. 

We dug a little deeper and found out that this user account had a log on restriction on it in local AD that was just implemented.

(this photo from my lab, hence not sanitized. I dont care if you try to compromise Zangief, the red cyclone will pile drive you)


Well there is our culprit. When using Pass-Thru Auth and you are doing log on locally restrictions you need to add whatever server the agent is on into the log on restrictions


Once the agent servers are added you should no longer be barred from accessing any other services. If you need to lock down your cloud services for these accounts that is where Conditional Access come into play. 

Moral of the story? Check your documentation when you make a change. This is laid out in the Pass-Thru Auth doc, although it is tucked away under the 'troubleshooting' doc and not the main concept or implementation document.


Hope this helps someone else out before they waste a few hours trying to figure out what the issue is.

Until next time everyone!