minimal PowerShell code to retrieve passwords from Windows Credentials

get-password.ps1

#
# PowerShell script to read out generic Windows Credentials
# this is kinda like macOS Keychain, but for Windows
#
# darell tan  2021.04.08
#

[String] $CredNativeCode = @"

using System;
using System.Runtime.InteropServices;

public class CredMan {
	[DllImport("Advapi32.dll", SetLastError=true, EntryPoint="CredReadW", CharSet=CharSet.Unicode)]
	private static extern bool CredReadW([In] string target, [In] uint type, [In] int flag, out IntPtr credential);

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

	[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Unicode)]
	private struct Credential {
		public uint Flags;
		public uint 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;
	}

	public static string GetCredPassword(string target) {
		IntPtr p;
		string password = null;
		if (CredReadW(target, /*GENERIC type*/ 1, 0, out p)) {
			Credential c = (Credential) Marshal.PtrToStructure(p, typeof(Credential));
			password = Marshal.PtrToStringUni(c.CredentialBlob, (int) (c.CredentialBlobSize / 2));
			CredFree(p);
		}
		return password;
	}
}
"@

Add-Type $CredNativeCode
$CredMan = [CredMan]

Write-Output "password" $CredMan::GetCredPassword("git:https://geekman@github.com")