Forefront TMG (Threat Management Gateway) formerly known as Microsoft Security and Acceleration Server (ISA server) is a Microsoft product that was typically used as a reverse proxy to securely publish internal applications and services to the internet.
It has been heavily used with Exchange, Sharepoint, Lync/ Skype for business and many applications hosted on Microsoft IIS.
As always you could build a solution from open source components, although due to the complexity and range of features required this should not be attempted by the faint hearted.
Or you could buy something -There are a number of top end ADC/ load balancers that also offer this with some being too complex and costly and others too simplistic and not fit for purpose.
Check out our Video and see how easy it is to use, or find out more on our website Pre-Authentication Feel free to test it out for Free on TESTDRIVE or download it for a trial.