I was able to get it working but it wasn't as straight forward as I thought it would have been. There's three things that need to happen

1. The account you're using to login with must exist in both Active Directory and Umbraco backoffice

2. Login using your active directory username rather than your company email address

3. Verify the domain that you set in the web.config file is correct - if it is wrong you won't be able to authenticate for obvious reasons.

If all of those conditions are satisfied and it's still not working then you can try what I did which is to take the class 'ActiveDirectoryBackOfficeUserPasswordChecker' from https://github.com/umbraco/Umbraco-CMS/blob/dev-v7/src/Umbraco.Core/Security/ActiveDirectoryBackOfficeUserPasswordChecker.cs and drop it in the file 'UmbracoStandardOwinStartup.cs' in the Umbraco solution in Visual Studio.

Then change the line userManager.BackOfficeUserPasswordChecker = new ActiveDirectoryBackOfficeUserPasswordChecker(); so that it points at the new class you just created in the UmbracoStandardOwinStartup.cs file

From here, it should be easy to debug your authentication issues just like you would in any other application. Good luck!

Note: I'm assuming you're trying to debug your Umbraco instance using IIS Express and that you've followed all the steps from https://our.umbraco.org/documentation/Reference/Security/#authenticating-with-active-directory-credentials

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