Demonstration of accepting credentials from a variable or file

Demonstrate-CredentialFile.ps1

<#
.SYNOPSIS
Demonstration of accepting credentials in a variable or file

.DESCRIPTION
This is only an demonstration of how a script can accept either a file
with stored credentials, or a PSCredential object, so that it can be used
performing tasks that require authentication.

.PARAMETER CredentialFile
Allows you to use a set of credentials stored in a file that was created like this.

    Get-Credential | Export-Clixml saved_credential.xml

.PARAMETER Credential
Accept a [System.Management.Automation.PSCredential] directly, so the script can still
be used by people with valid credentials that don't have a saved file

.EXAMPLE
Get your credentials and call the script

    Get-Credential | Export-Clixml saved_credential.xml
    .\Demonstrate-CredentialFile.ps1 -CredentialFile saved_credential.xml

.EXAMPLE
Get your credentials and call the script

    $creds = Get-Credential
    .\Demonstrate-CredentialFile.ps1 -Credential $creds

.NOTES

Invoke-ScriptAnalyzer Demonstrate-CredentialFile.ps1 reports a
warning `PSAvoidUsingPlainTextForPassword` for having a paramater named
`$CredentialFile` being used as a simple string.  This is a **false-positive**.
This is not a path to a file, not a username/password/pscredential.

The credentials file used here will be encrypted using the Windows Crypto API.
A secret will be part of the profile, which means it will only be useable on
the machine, under the specific profile that the credential file was saved.

Since this file is linked to a specific profile, it probably should be saved in
the profile directory So something like:

    c:\Users\username\Documents\credentialpurpose_credential.xml

#>

[cmdletBinding()]
param(
[parameter(ParameterSetName='CredVar',
           Mandatory=$true)]
          [pscredential]
          [System.Management.Automation.CredentialAttribute()]
          $Credential,
[parameter(ParameterSetName='CredFile',
           Mandatory=$true)]
          [string]$CredentialFile
)
Set-StrictMode -Version Latest

# Get Credentials when CredentialFile was used.
If ('CredFile' -eq $PsCmdlet.ParameterSetName) {
    $Credential = Import-Clixml $CredentialFile
    If ('System.Management.Automation.PSCredential' -ne
        ($Credential).GetType().FullName) {
        throw "The loaded object must be a [System.Management.Automation.PSCredential]"
    }
}

$Credential