Get-CredentialFromWindowsCredentialManager.ps1

<# 
The MIT License

Copyright (c) 2012 Tobias Burger
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation 
files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, 
merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is 

furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT 
LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN 
NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE 
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


Downloaded from from https://gist.github.com/toburger/2947424 there is a fork designed to load as a module at https://gist.github.com/toburger/2947424
Changelog from Downloaded version 
  Added PlainTextPasswordOnly switch and the line if ($PlainTextPasswordOnly) {return $cred.CredentialBlob} 
  Wrapped Add-Type in try {} / Catch{}
#>


<#
    .SYNOPSIS
    Gets a PowerShell Credential (PSCredential) from the Windows Credential Manager

    .DESCRIPTION
    Adapted from: http://stackoverflow.com/questions/7162604/get-cached-credentials-in-powershell-from-windows-7-credential-manager

    .PARAMETER TargetName
    The name of the target login informations in the Windows Credential Manager

    .EXAMPLE
    .\Get-CredentialFromWindowsCredentialManager.ps1 tfs.codeplex.com

    UserName                             Password
    --------                             --------
    codeplexuser                         System.Security.SecureString

    .LINK
    Get-Credential
#>
param([Parameter(Mandatory=$true)][string]$TargetName, [switch]$PlainTextPasswordOnly)

$sig = @"

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct NativeCredential
{
    public UInt32 Flags;
    public CRED_TYPE Type;
    public IntPtr TargetName;
    public IntPtr Comment;
    public System.Runtime.InteropServices.ComTypes.FILETIME LastWritten;
    public UInt32 CredentialBlobSize;
    public IntPtr CredentialBlob;
    public UInt32 Persist;
    public UInt32 AttributeCount;
    public IntPtr Attributes;
    public IntPtr TargetAlias;
    public IntPtr UserName;

    internal static NativeCredential GetNativeCredential(Credential cred)
    {
        NativeCredential ncred = new NativeCredential();
        ncred.AttributeCount = 0;
        ncred.Attributes = IntPtr.Zero;
        ncred.Comment = IntPtr.Zero;
        ncred.TargetAlias = IntPtr.Zero;
        ncred.Type = CRED_TYPE.GENERIC;
        ncred.Persist = (UInt32)1;
        ncred.CredentialBlobSize = (UInt32)cred.CredentialBlobSize;
        ncred.TargetName = Marshal.StringToCoTaskMemUni(cred.TargetName);
        ncred.CredentialBlob = Marshal.StringToCoTaskMemUni(cred.CredentialBlob);
        ncred.UserName = Marshal.StringToCoTaskMemUni(System.Environment.UserName);
        return ncred;
    }
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct Credential
{
    public UInt32 Flags;
    public CRED_TYPE Type;
    public string TargetName;
    public string Comment;
    public System.Runtime.InteropServices.ComTypes.FILETIME LastWritten;
    public UInt32 CredentialBlobSize;
    public string CredentialBlob;
    public UInt32 Persist;
    public UInt32 AttributeCount;
    public IntPtr Attributes;
    public string TargetAlias;
    public string UserName;
}

public enum CRED_TYPE : uint
    {
        GENERIC = 1,
        DOMAIN_PASSWORD = 2,
        DOMAIN_CERTIFICATE = 3,
        DOMAIN_VISIBLE_PASSWORD = 4,
        GENERIC_CERTIFICATE = 5,
        DOMAIN_EXTENDED = 6,
        MAXIMUM = 7,      // Maximum supported cred type
        MAXIMUM_EX = (MAXIMUM + 1000),  // Allow new applications to run on old OSes
    }

public class CriticalCredentialHandle : Microsoft.Win32.SafeHandles.CriticalHandleZeroOrMinusOneIsInvalid
{
    public CriticalCredentialHandle(IntPtr preexistingHandle)
    {
        SetHandle(preexistingHandle);
    }

    public Credential GetCredential()
    {
        if (!IsInvalid)
        {
            NativeCredential ncred = (NativeCredential)Marshal.PtrToStructure(handle,
                  typeof(NativeCredential));
            Credential cred = new Credential();
            cred.CredentialBlobSize = ncred.CredentialBlobSize;
            cred.CredentialBlob = Marshal.PtrToStringUni(ncred.CredentialBlob,
                  (int)ncred.CredentialBlobSize / 2);
            cred.UserName = Marshal.PtrToStringUni(ncred.UserName);
            cred.TargetName = Marshal.PtrToStringUni(ncred.TargetName);
            cred.TargetAlias = Marshal.PtrToStringUni(ncred.TargetAlias);
            cred.Type = ncred.Type;
            cred.Flags = ncred.Flags;
            cred.Persist = ncred.Persist;
            return cred;
        }
        else
        {
            throw new InvalidOperationException("Invalid CriticalHandle!");
        }
    }

    override protected bool ReleaseHandle()
    {
        if (!IsInvalid)
        {
            CredFree(handle);
            SetHandleAsInvalid();
            return true;
        }
        return false;
    }
}

[DllImport("Advapi32.dll", EntryPoint = "CredReadW", CharSet = CharSet.Unicode, SetLastError = true)]
public static extern bool CredRead(string target, CRED_TYPE type, int reservedFlag, out IntPtr CredentialPtr);

[DllImport("Advapi32.dll", EntryPoint = "CredFree", SetLastError = true)]
public static extern bool CredFree([In] IntPtr cred);


"@
try { Add-Type -MemberDefinition $sig -Namespace "ADVAPI32" -Name 'Util'}
catch {if ($_.FullyQualifiedErrorId -notmatch "TYPE_ALREADY_EXISTS") {throw $_ } } 


$nCredPtr= New-Object IntPtr

$success = [ADVAPI32.Util]::CredRead($TargetName,1,0,[ref] $nCredPtr)

if ($success) {
    $critCred = New-Object ADVAPI32.Util+CriticalCredentialHandle $nCredPtr
    $cred = $critCred.GetCredential()
    if ($PlainTextPasswordOnly) {return $cred.CredentialBlob}
    $username = $cred.UserName
    $securePassword = $cred.CredentialBlob | ConvertTo-SecureString -AsPlainText -Force
    $cred = $null
    return new-object System.Management.Automation.PSCredential $username, $securePassword
} 
else {
    Write-Error "No credentials where found in Windows Credential Manager for TargetName: $TargetName"
}