We were setting up a couple of servers with a Exchange DAG and Remote Desktop Gateway services and ran in to an issue where the Remote Desktop Gateway was looping on asking for credentials.
A fair bit of searching eventually turned up a hint that RPC authentication was set to Basic only and it needed NTLM as well.
So you set the authentication to Basic and NTLM and think you’re done, but 5 minutes later it’s been reset to Basic only and you’re left wondering what’s going on.
A bit more searching highlighted that it was Exchange that was reseting the authentication methods and to make Exchange stop doing that you can run the following PowerShell command:
Get-OutlookAnywhere | Set-OutlookAnywhere -IISAuthenticationMethods: Basic, ntlm