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How do I change system time from a non elevated c# program

I need your help again :)
What I want to do:
I have a c# program which runs with normal user permissions - those can't be raised - and I want to change the system date (not time) from that program.
[EDIT] To be a bit more specific: I do have administrator credentials which could be embedded to the program (yikes, I know), but I want to avoid an UAC prompt.
When I launch cmd from outside Visual Studio and try to change the date, it fails with "missing client permission" (roughly translated from German). When I launch cmd as administrator, confirm the UAC prompt the same command succeeds.
I am writing from home, so I cant provide running code at the moment. But all my tries did compile and run without error but the date wasn't changed.
What I've tried:
Created a Process instance, applied admin credentials to ProcessStartInfo, set the FileName to c:\windows\system32\cmd.exe and the argument to /C date {thedate}. I redirected StandardOutput and StandardError and after execution StandardError contains the same message as stated above: "missing client permission"
I've modified this example MSDN: WindowsIdentity.Impersonate using PInvoke with AdvAPI32.LogonUser to raise permissions and Kernel32.SetSystemTime to change the system time. AdvAPI32.LogonUser succeeds and WindowsIdentity.GetCurrent().Name returns the admin name, but calling Kernel32.SetSystemTime fails with "missing client permission".
I've tried opening the current process AdvApi32.OpenCurrentProcess and adjusting the permissions using AdvApi32.AdjustTokenPrivileges following this example StackOverflow: Change system time programmaticaly using datetimepeaker and the code runs totally fine but Kernel32.SetSystemTime fails...
[EDIT] Solution:
I ended up writing a small program with an embedded app.manifest that requests administrator privilegs. This app is called from the main program so this can still be run by a normal user.

It is not possible to change the privileges of the process, once it's started. The original process has to start another process with elevated privileges. This second process can actually be the same .exe file, but with a command parameter that tells the process to do some small stuff and exit immediately.
To start a process with elevated privileges use Process.Start, but with .Verb = "runas", as described in another question. This will of course cause UAC prompt to pop up, if it's enabled on the machine. At least one UAC prompt has to be shown, because UAC prompt is the whole point if this defense mechanism.
If you want to reduce many UAC prompts to just one then you can set the original app to be started as administrator (UAC prompt shows when original process starts) and have just one process. Or have some interprocess communication between original process and elevated process, so that elevated process is started only once and made to finish when original process ends. In the second case UAC prompt shows the first time it's needed.

Can I ask why you are needing to change the system time from an unprivileged application?
If it is to influence other applications then you will need admin privilege since date time is such a vital system function to many other applications. However if you are just needing to adjust the date in your application only then I would suggest creating your own date/time provider that can return the date offset to the date that you desire in your application.
For example.
public DateTime GetDateWithOffset(int daysToOffset)
{
return DateTime.UtcNow.AddDays(daysToOffset);
}

Secure password communication between 2 applications

I am writing a program, which is like a swiss army knife of tools that my colleagues need in their day to day work. One feature of this tool is, to be able to connect to a client remotely and control it.
We already have an application called Dameware Mini Remote Control, not written by us, that does this exact job. My application just starts this software in a process and hands over username and password, the user has entered beforehand.
In the documentation of the Dameware Tool, it says that the process should be called with these arguments:
"dwrcc.exe [-?|-?:] [-c:] [-h:] [-m:MachineName] [-u:UserName] [-p:Password | -p:"Password"] [-d:Domain] [-o:TCPport] [-s:SharedSecret] [-r:] [-vnc:] [-a:0|1|2] [-prxa:MRCproxyAddress] [-prxp:MRCproxyPort] [-prxsMRCproxySecret] [-v:] [-md:] [-i:n] [-x:] [-bh:CentralServerHostAddress] [-bpn: CentralServerPortNumber] [-bu:CentralServerUserName] [-bps:CentralServerUserPassword]"
My concern is that providing the password in the -p option is not secure, because it is basically plain text.
Here is the part of my code where i provide the command line arguments:
proc.StartInfo.Arguments = $"-c: -h: -x: -m:{TxtHostname} -d:{MainUI.Credentials.DomainName} -u:{MainUI.Credentials.UserName} -p:{LoginCredentials.Decrypt(MainUI.Credentials.EncryptedPassword)}";
Is there a secure way of handing over the password to the Dameware application inside the process?
Any suggestions are greatly appreciated.

This is not possible in general. If the only option is to pass the password via a command line parameter, you do only have this option.
However it would be possible if the target application supports another way of receiving the password. This is application specific and doesn't apply to every application.
As I'm not familiar with Dameware Mini Remote Control, I can't tell if such an option exists in this specific case.

Launch a process with the "Run As..." dialog

I've got an application that uses the current user credentials to connect to a server and run some performance tests.
For numerous reasons, impersonation isn't a viable option. Instead, I'd like to give the user a "Switch User" button which re-launches the process but shows the Run As... dialog.
I can't see an option on Process.Start() or the Associated ProcessStartInfo. There is an option to provide a username/password I've captured but I'd rather not be involved in the process at all and just let windows handle it. Just using the runas verb merely prompts to elevate but if the current user is a local admins, there's no option to provide a different username.
Is there a way to do this? I know there's a command-line runas.exe but that's not a great user experience

Have you looked at the process.start() documentation? Never tried this, but looks like they have you covered:
public static Process Start(
string fileName,
string userName,
SecureString password,
string domain
)
https://msdn.microsoft.com/en-us/library/sxf2saat%28v=vs.110%29.aspx

How to run a non-admin process from admin c# application

I have a c# application that needs to do some things as an admin (some installation stuff) and then it needs to run another process as a non-admin. I haven't done anything with UAC before, but I assume there must be a way to do this, right?
This also needs to be automated, so assume that the c# app is started with admin credentials.
Basically the program will need to do something like this:
// MUST run this process as admin
Process adminInstall = new Process();
adminInstall.StartInfo.FileName = "install.bat";
adminInstall.Start();
adminInstall.WaitForExit();
// CANNOT run this process as admin
Process nonAdminProcess = new Process();
nonAdminProcess.StartInfo.FileName = "runner.cmd";
nonAdminProcess.StartInfo.UseShellExecute = false;
nonAdminProcess.StartInfo.RedirectStandardOutput = true;
nonAdminProcess.OutputDataReceived += new DataReceivedEventHandler(myHandler);
nonAdminProcess.Start();
nonAdminProcess.BeginOutputReadLine();
nonAdminProcess.WaitForExit();

You can embed a manifest in the executable using MT.exe (manifest tool) in the platform SDK after the binary is compiled, but before it is signed. You also have the option of using a custom manifest within your project properties. Open the project properties, then go to the application tab, then change the manifest option from default manifest, to custom manifest. Visual Studio will add a manifest to your project where you can specify "requireAdministrator" privleges. When your app runs, it will provide a UAC prompt, or ask for credentials if logged on as user. There is a good chance sub process will start as admin as well. Otherwise you will need to launch them with the "runas" verb which is undocumented.

Process.Start parameters has one for Username. See Process.Start reference:
http://msdn.microsoft.com/en-us/library/sxf2saat.aspx

There does not appear to be a nice way of doing this using the .Net classes. However, Process.Start with different credentials with UAC on explains a way of doing it using CreateProcessAsUserW after stealing a handle from another process.

If the aforementioned methods aren't viable, then you can try my method. But its ugly; you need to get a handle to a non admin process, then use DuplicateTokenEx (p/invoke) to copy its (non admin) privileges, then pass that into CreateProcessAsUser. You first need to identify a non admin process though, there may not be any. The newly created process will be spawned with whatever privileges the token you copied contained, not the token of the parent process.

Interactively log on another Windows user from c# code

I am trying to achive a situation:
I am logged as a user on my account.
I've created a two more accounts which I will try to log on in the
"background"
And now I want to execute my code to log on different user in the background,
so that if i can click ctrl+alt+del and go to the switch user screen
i can see that another account was logged on the system.
During investigation I've read that this was possbile with some undocumented winapi methods before Microsoft implemented Fast User Switch(FUS) which replaced GINA.
I don't want to Impersonate code as user. I want to start up the whole windows session for a user from code.
I've tried to do sth with CreateProcessWithLogonW() but this was unsuccessful.
Big virtual beer for anybody who can give me a hand with this! :)

Okay had to do a bit of digging to figure this out my self.
Essentially you would need to run a command in command prompt.
This should load explorer.exe as a second user.
runas /user:*computer name\*account name explorer.exe
Follow this to get an idea on running a command line command via c#:
How To: Execute command line in C#, get STD OUT results
Other sources:
http://www.computerhope.com/runas.htm
http://lifehacker.com/290435/switch-user-accounts-from-the-command-prompt