POSTS

Using ScriptProperty members in PowerShell

March 25, 2009

I was looking for information on ScriptProperty members in PowerShell and was running into trouble finding anything useful. The PowerShell in Action book saved me on page 229.

Here is the object I am using in a piece of code that I am finishing for persisting server credentials to disk in a secure fashion. It shows a real world example of when a ScriptProperty is needed instead of the simpler NoteProperty.

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Function SecureCredentialStoreItem
{
    $item = New-Object PSObject
    
    # Hostname
    $item | Add-Member -MemberType NoteProperty -Name hostname -Value ""
    
    # Username portion of the credential
    $item | Add-Member -MemberType ScriptProperty -Name username -Value `
            { # Get
                $this.credential.username
            } `
            { # Set
            
                param
                (
                    [String]$username
                )
                
                # Username is read only so we create a replacement credential.
                $newCred = New-Object System.Management.Automation.PSCredential $username, $this.credential.password
                $this.credential = $newCred
            }
    
    # Password portion of the credential
    $item | Add-Member -MemberType ScriptProperty -Name password -Value `
            { # Get
                $this.credential.password
            } `
            { # Set
            
                param 
                (
                    [System.Security.SecureString]$password
                )
                               
                # Password is read only so we create a replacement credential.
                $newCred = New-Object System.Management.Automation.PSCredential $this.credential.username, $password
                $this.credential = $newCred
            }
    
    # Credential
    $item | Add-Member -MemberType NoteProperty -Name credential -Value `
                       (New-Object System.Management.Automation.PSCredential "&lt;empty>", 
                            (New-Object System.Security.SecureString))

    # In general I would recommend against using this, but there are times
    # when it must be done.  Done as a method so it is not run unless called
    # explicitly.  Setting should be done via the securestring password property.
    $item | Add-Member -MemberType ScriptMethod -Name passwordToPlainText -Value `
            {
                $ptr=[System.Runtime.InteropServices.Marshal]::SecureStringToCoTaskMemUnicode($this.credential.password)
                $str = [System.Runtime.InteropServices.Marshal]::PtrToStringUni($ptr)
                [System.Runtime.InteropServices.Marshal]::ZeroFreeCoTaskMemUnicode($ptr)
                $str
            }
    $item
}