Topshelf install, PowerShell and Get-Credentials

In the project I’m currently working at we use PowerShell script for configuration and build execution.

This means that if you get a new laptop, or a new member joins the team, or even when you need to change your Windows password, you just need to run the script again and it will set up everything in the correct locations & with the correct credentials.

The credentials were a problem though.

When installing a Topshelf service with the --interactive parameter (we need to install under the current user, not System) it will prompt you for your credentials for each service you want to install. For one, it’s fine, for 2, it’s already boring, for 3, … You get the point.

We initially used the following command line to install the services:

. $pathToServiceExe --install --interactive --autostart

To fix this we will give the $pathToServiceExe the username and password ourselves with the -username and -password. We should also omit the --interactive.

First gotcha here: When reading the documentation, it says one must specify the commands in this format:

. $pathToServiceExe --install --autostart -username:username -password:password

However, this is not the case. You mustn’t separate the command line argument and the value with a :.

Now, we don’t want to hardcode the username & password file in the setup script.

So let’s get the credentials of the current user:

$credentialsOfCurrentUser = Get-Credential -Message "Please enter your username & password for the service installs"

Next up we should extract the username & password of the $credentialsOfCurrentUser variable, as we need it in clear-text (potential security risk!).

One can do this in 2 ways, either by getting the NetworkCredential from the PSCredential with GetNetworkCredential():

$networkCredentials = $credentialsOfCurrentUser.GetNetworkCredential();
$username = ("{0}\{1}") -f $networkCredentials.Domain, $networkCredentials.UserName # change this if you want the user@domain syntax, it will then have an empty Domain and everything will be in UserName. 
$password = $networkCredentials.Password

Notice the $username caveat.

Or, by not converting it to a NetworkCredential:

# notice the UserName contains the Domain AND the UserName, no need to extract it separately
$username = $credentialsOfCurrentUser.UserName

# little more for the password
$BSTR = [System.Runtime.InteropServices.Marshal]::SecureStringToBSTR($credentialsOfCurrentUser.Password)
$password = [System.Runtime.InteropServices.Marshal]::PtrToStringAuto($BSTR)

Notice the extra code to retrieve the $password in plain-text.

I would recommend combining both, using the NetworkCredential for the $password, but the regular PSCredential for the $username as then you’re not dependent on how your user enters his username.

So the best version is:

$credentialsOfCurrentUser = Get-Credential -Message "Please enter your username & password for the service installs" 
$networkCredentials = $credentialsOfCurrentUser.GetNetworkCredential();
$username = $credentialsOfCurrentUser.UserName
$password = $networkCredentials.Password

Now that we have those variables we can pass them on to the install of the Topshelf exe:

. $pathToServiceExe install -username `"$username`" -password `"$password`" --autostart

Notice the backticks (`) to ensure the double quotes are escaped.

In this way you can install all your services and only prompt your user for his credentials once!