Winsta | Unofficial Windows INSTAgram client/UWP | iOS library

I'm trying to call CreateProcessAsUser to run a desktop application for a user from a service. (See Launching a process in user’s session from a service and CreateProcessAsUser from service and user security issues)

It basically works, but some applications fail to run properly. Ultimately after some debugging I found out that one C# application fails because Environment.GetFolderPath returns null for a special folder. I'm thinking that this could be because the invoked user's registry or some paths in it are not correctly loaded for the user profile.

In the REMARKS section of CreateProcessAsUserW there are a few hints what to consider when creating a process for a user. I'm already creating an environment block using CreateEnvironmentBlock (and the environment variables seem to work), but it also says:

CreateProcessAsUser does not load the specified user's profile into the HKEY_USERS registry key. Therefore, to access the information in the HKEY_CURRENT_USER registry key, you must load the user's profile information into HKEY_USERS with the LoadUserProfile function before calling CreateProcessAsUser. [...]

I have checked the documentation of LoadUserProfile where it says something similar:

Note that it is your responsibility to load the user's registry hive into the HKEY_USERS registry key with the LoadUserProfile function before you call CreateProcessAsUser. This is because CreateProcessAsUser does not load the specified user's profile into HKEY_USERS. This means that access to information in the HKEY_CURRENT_USER registry key may not produce results consistent with a normal interactive logon.

However I didn't find any example or further details how to load a user's registry hive into the HKEY_USERS registry key and the registry APIs I looked at (RegLoadKey looked most promising, but I don't think that's the correct one or how to use it with a my target process before CreateProcessAsUser) don't do what is described on LoadUserProfile. Furthermore all StackOverflow questions I looked at didn't mention this or only just mentioned on the side that they are using this function.

I thought maybe passing the profile could be part of STARTUPINFOEX but I also didn't find anything regarding "profile" or "registry" in the documentation there.

I'm really struggling trying to find out what to do with the LoadUserProfile result (struct PROFILEINFO) and how to use it with the CreateProcessAsUserW function. I would be glad if you could give me some hints what I actually want to do with that function and how I can use it with CreateProcessAsUserW given that I have already acquired a user token with WTSQueryUserToken.

This is my current C# code how I spawn the process (it also contains some piping code which I left out for readability):