On Disk Credentials

This article has been written by plenty of people, plenty of times. But even so, I’m writing it again. This is partly because I want to have a place to find this information written by myself. That said, if it helps anyone else too, then it’s doing the other part, and that’s helping those around me.

What I want to do today, is create an on disk credential file. I’ve done it a few times now, for a few projects, but there’s something about this topic, I can’t forever nail down in my own brain. Well, as best as I see it, those days are numbered.

Once my on disk credential file is created, I want to run an automated task(s) as a user other than that which is running my outlying automation. It’s kind of like this: User1 runs an automated task and it needs to complete some work it can’t do on it’s own. Therefore, it does a part of what it needs as User2. That’s the user that can do what User1 can’t.

The first step is creating the credential file. Now, when you think of credentials, you should think of the combination of a username and a corresponding password, together. That said, this credential file is actually only going to hold the password. While I’m going to continue to call it a credential file, keep in mind that we’re only storing the password inside this file.

In the below example, we’re taking a password, as a standard string, converting it to a secure string, converting that (the secure string) into an encrypted standard string, and writing it out to an on disk file. Before we begin, we need to open our PowerShell host (the ConsoleHost, the ISE, etc.). Based on User1 and User2, we’d open PowerShell as User1. Remember, User1 is going to run our script, function, automation, etc., but it’s going to require creating a credential object — a username and password — for User2.

One other consideration to keep in mind is the computer on which this password file will be used. You have to use the credential file on the computer in which it’s created, and with the user that created it.

$PasswordAsString = '1234)(#DGTh@ppYMedixM.'
$PassOut = ConvertTo-SecureString -String $PasswordAsString -AsPlainText -Force
$PassOut | ConvertFrom-SecureString | Out-File -FilePath 'C:\Users\tommymaynard\Desktop\cred.txt'

Here’s what each line in the above example accomplishes:

Line 1: Creates a variable to hold the password as a standard string. A standard string is like any other string, such as the word dog, cat, or house. Each of those is a standard string, and most often just called a string. We’re including the word “standard,” as a way to differentiate among the other string types we’ll discuss.
Line 2: Creates a variable to hold the password once it’s been converted to a secure string. The AsPlainText and Force parameters are required for ConvertTo-SecureString to accept a standard sting for conversion.
Line 3: Converts the password as stored in the variable created in Line 2 as a secure string, to an encrypted standard string and saves it in an on disk file called cred.txt on my desktop.

Here’s the thing: The above process is a one time thing. Once the on disk credential file is created, then that step will never have to be duplicated (unless you change User2’s password). Remember, you have to open PowerShell as the user that will use the password, not as the account to which the password corresponds.

The next bit of code is how we use the on disk credential file.

$User = 'domain\User2'
$PassIn = Get-Content -Path 'C:\Users\tommymaynard\Desktop\cred.txt' | ConvertTo-SecureString
$Credential = New-Object System.Management.Automation.PSCredential -ArgumentList $User,$PassIn

Here’s what each line in this example accomplishes:

Line 1: Creates a variable to hold the username of the user that corresponds to this password.
Line 2: Creates a variable to hold the password. This command will read in the contents of our cred.txt file from our first example, and convert the encrypted standard string in the file to secure string.
Line 3: Creates a variable to store the credential object. This includes both the username from line 1, and the password we brought in from line 2.

That’s it. Again, this is a two step process. The first example was how to prestage our credential file, and the second example allows us to make use of it. The first example would likely be done once, manually, and as part of a prestaging effort. The second example would be done inside of the script, etc., to make use of running something as a user (User2) other than the one running the script, etc. itself (User1).

Okay Tommy, you now have a place to turn once you’re forgotten how to do this. You too, Internet.

2 thoughts on “On Disk Credentials

  1. Jonathan Angliss

    Have you checked out Import/Export-CliXML? It converts an object to XML and outputs to a file. You can pull in both username and password in one step. Same rules apply with SecureString in that you have to access the file using the same account that created the file. Its usage is fairly simple, like Import/Export-CSV:

    $creds = Get-Credentials
    $creds | Export-CliXML test1.creds

    $newCreds = Import-CliXML test1.creds

    I’ve found it super handy.

    Reply
    1. tommymaynard Post author

      Hey Jon,

      I certainly have used Import-/Export-CliXml; however, I’ve only used it to capture error ($Error) messages. It’s almost easier to read though an error message this way. What I haven’t done is used it for credentials. That said, I’m going to keep it in mind for the next time I’m down the credential road again! Thanks for your contribution, Jon.

      Tommy

      Reply

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