Vanara/Windows.Forms/Dialogs/CredentialsDialog/AuthenticationBuffer.cs

using System.ComponentModel;
using System.Diagnostics.CodeAnalysis;
using System.Security;
using Vanara.PInvoke;
using static Vanara.PInvoke.CredUI;

namespace Vanara.Security;

/// <summary>
/// Safe container for an authentication buffer. Allows for creation using native <c>CredPackAuthenticationBuffer</c> method or
/// assignment from an existing <c>IntPtr</c>. Can unpack to <see cref="string"/> or <see cref="SecureString"/> values.
/// </summary>
public class AuthenticationBuffer : IDisposable
{
	private SafeCoTaskMemHandle buffer;

	/// <summary>Initializes a new instance of the <see cref="AuthenticationBuffer"/> class.</summary>
	/// <param name="userName">Name of the user.</param>
	/// <param name="password">The password.</param>
	public AuthenticationBuffer(string? userName, string? password) => Init(0, userName, password);

	/// <summary>Initializes a new instance of the <see cref="AuthenticationBuffer"/> class.</summary>
	/// <param name="userName">Name of the user.</param>
	/// <param name="password">The password.</param>
	public AuthenticationBuffer(SecureString? userName, SecureString? password)
	{
		var pUserName = userName is null ? SafeCoTaskMemString.Null : new SafeCoTaskMemString(userName);
		var pPassword = password is null ? SafeCoTaskMemString.Null : new SafeCoTaskMemString(password);
		Init(0, pUserName, pPassword);
	}

	/// <summary>Initializes a new instance of the <see cref="AuthenticationBuffer"/> class.</summary>
	/// <param name="authBuffer">The authentication buffer.</param>
	/// <param name="authBufferSize">Size of the authentication buffer.</param>
	public AuthenticationBuffer(IntPtr authBuffer, int authBufferSize) => buffer = new SafeCoTaskMemHandle(authBuffer, authBufferSize);

	/// <summary>Gets the dangerous handle.</summary>
	/// <value>The dangerous handle.</value>
	public IntPtr DangerousHandle => buffer?.DangerousGetHandle() ?? IntPtr.Zero;

	/// <summary>Gets the size.</summary>
	/// <value>The size.</value>
	public int Size => buffer?.Size ?? 0;

	/// <summary>Performs an implicit conversion from <see cref="AuthenticationBuffer"/> to <see cref="IntPtr"/>.</summary>
	/// <param name="b">The b.</param>
	/// <returns>The resulting <see cref="IntPtr"/> instance from the conversion.</returns>
	public static implicit operator IntPtr(AuthenticationBuffer b) => b.DangerousHandle;

	/// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
	public void Dispose()
	{
		buffer.Zero();
		GC.SuppressFinalize(this);
	}

	/// <summary>Unpacks the credentials.</summary>
	/// <param name="decryptProtectedCredentials">if set to <see langword="true"/> decrypt protected credentials.</param>
	/// <param name="userName">Name of the user.</param>
	/// <param name="domainName">Name of the domain.</param>
	/// <param name="password">The password.</param>
	/// <exception cref="Win32Exception"></exception>
	public void UnPack(bool decryptProtectedCredentials, out string userName, out string? domainName, out string password)
	{
		var pUserName = new StringBuilder(CRED_MAX_USERNAME_LENGTH);
		var pDomainName = new StringBuilder(CRED_MAX_USERNAME_LENGTH);
		var pPassword = new StringBuilder(CREDUI_MAX_PASSWORD_LENGTH);
		var userNameSize = pUserName.Capacity;
		var domainNameSize = pDomainName.Capacity;
		var passwordSize = pPassword.Capacity;

		if (!CredUnPackAuthenticationBuffer(decryptProtectedCredentials ? CredPackFlags.CRED_PACK_PROTECTED_CREDENTIALS : 0x0, DangerousHandle, Size,
			pUserName, ref userNameSize, pDomainName, ref domainNameSize, pPassword, ref passwordSize))
			throw new Win32Exception();

		userName = pUserName.ToString();
		domainName = domainNameSize == 0 ? null : pDomainName.ToString();
		password = pPassword.ToString();
	}

	/// <summary>Unpacks the credentials.</summary>
	/// <param name="decryptProtectedCredentials">if set to <see langword="true"/> decrypt protected credentials.</param>
	/// <param name="userName">Name of the user.</param>
	/// <param name="domainName">Name of the domain.</param>
	/// <param name="password">The password.</param>
	/// <exception cref="Win32Exception"></exception>
	public void UnPack(bool decryptProtectedCredentials, out SecureString userName, out SecureString? domainName, out SecureString password)
	{
		var pUserName = new SafeCoTaskMemString(CRED_MAX_USERNAME_LENGTH);
		var pDomainName = new SafeCoTaskMemString(CRED_MAX_USERNAME_LENGTH);
		var pPassword = new SafeCoTaskMemString(CREDUI_MAX_PASSWORD_LENGTH);
		var userNameSize = pUserName.Capacity;
		var domainNameSize = pDomainName.Capacity;
		var passwordSize = pPassword.Capacity;

		if (!CredUnPackAuthenticationBuffer(decryptProtectedCredentials ? CredPackFlags.CRED_PACK_PROTECTED_CREDENTIALS : 0x0, DangerousHandle, Size,
			(IntPtr)pUserName, ref userNameSize, (IntPtr)pDomainName, ref domainNameSize, (IntPtr)pPassword, ref passwordSize))
			throw new Win32Exception();

		userName = pUserName.DangerousGetHandle().ToSecureString()!;
		domainName = domainNameSize == 0 ? null : pDomainName.DangerousGetHandle().ToSecureString();
		password = pPassword.DangerousGetHandle().ToSecureString()!;
	}

	[MemberNotNull(nameof(buffer))]
	private void Init(CredPackFlags flags, string? pUserName, string? pPassword)
	{
		var bufferSize = 0;
		if (!CredPackAuthenticationBuffer(flags, pUserName ?? "", pPassword ?? "", IntPtr.Zero, ref bufferSize) && Win32Error.GetLastError() == Win32Error.ERROR_INSUFFICIENT_BUFFER)
		{
			buffer = new SafeCoTaskMemHandle(bufferSize);
			if (!CredPackAuthenticationBuffer(flags, pUserName ?? "", pPassword ?? "", DangerousHandle, ref bufferSize))
				throw new Win32Exception();
		}
		else
			throw new Win32Exception();
	}
}