We have a non-domain joined SQL 2012 server running in Azure supporting several web sites, earlier this week an issue popped up where domain joined computers could not log in. There were no updates or changes applied to the server, no login errors, fiddler showed no issues. The user accounts were able to login from outside the domain network.
In order to resolve the issue I had to edit C:\Program Files\Microsoft SQL Server\MSRS11.MSSQLSERVER\Reporting Services\ReportServer\reportserver.xml
Comment out the following:
<!--<RSWindowsNTLM/>--> <!--<RSWindowsNegotiate/>--> <RSWindowsBasic/>
Leaving WindowsBasic as the only authentication type.
I'm not sure as to why this popped up as an issue as nothing else changed, and if anyone has some insight I would appreciate it. But this is a solution for anyone that experiences the same issue.