Following on from the previous blog post, if you can't map arbitrary SIDs to names to make displaying capabilities nicer what is the purpose of LsaManageSidNameMapping? The primary purpose is to facilitate the creation of Virtual Service Accounts. 

A virtual service account allows you to create an access token where the user SID is a service SID, for example, NT SERVICE\TrustedInstaller. A virtual service account doesn't need to have a password configured which makes them ideal for restricting services rather than having to deal with the default service accounts and using WSH to lock them down or specifying a domain user with password.

To create an access token for a virtual service account you can use LogonUserExEx and specify the undocumented (AFAIK) LOGON32_PROVIDER_VIRTUAL logon provider. You must have SeTcbPrivilege to create the token, and the SID of the account must have its first RID in the range 80 to 111 inclusive. Recall from the previous blog post this is exactly the same range that is covered by LsaManageSidNameMapping.

The LogonUserExEx API only takes strings for the domain and username, you can't specify a SID. Using the LsaManageSidNameMapping function allows you to map a username and domain to a virtual service account SID. LSASS prevents you from using RID 80 (NT SERVICE) and 87 (NT TASK) outside of the SCM or the task scheduler service (see this snippet of reversed LSASS code for how it checks). However everything else in the RID range is fair game.

So let's create out own virtual service account. First you need to add your domain and username using the tool from the previous blog post. All these commands need to be run as a user with SeTcbPrivilege.

SetSidMapping.exe S-1-5-100="AWESOME DOMAIN" 
SetSidMapping.exe S-1-5-100-1="AWESOME DOMAIN\USER"

So we now have the AWESOME DOMAIN\USER account with the SID S-1-5-100-1. Now before we can login the account you need to grant it a logon right. This is normally SeServiceLogonRight if you wanted a service account, but you can specify any logon right you like, even SeInteractiveLogonRight (sadly I don't believe you can actually login with your virtual account, at least easily).

If you get the latest version of NtObjectManager (from github at the time of writing) you can use the Add-NtAccountRight command to add the logon type.

PS> Add-NtAccountRight -Sid 'S-1-5-100-1' -LogonType SeInteractiveLogonRight

Once granted a logon right you can use the Get-NtToken command to logon the account and return a token.

PS> $token = Get-NtToken -Logon -LogonType Interactive -User USER -Domain 'AWESOME DOMAIN' -LogonProvider Virtual

PS> Format-NtToken $token
AWESOME DOMAIN\USER

As you can see we've authenticated the virtual account and got back a token. As we chose to logon as an interactive type the token will also have the INTERACTIVE group assigned. Anyway that's all for now. I guess as there's only a limited number of RIDs available (which is an artificial restriction) MS don't want document these features even though it could be a useful thing for normal developers.