FTP and LDAP - Part 1: How to Use Managed Code (C#) to Create an FTP Authentication Provider that uses an LDAP Server

Over the past few years I've created a series of authentication providers for the FTP 7.5 service that ships with Windows Server 2008 R2 and Windows 7, and is available for download for Windows Server 2008. Some of these authentication providers are available on the http://learn.iis.net/page.aspx/590/developing-for-ftp-75/ website, while others have been in my blog posts.

With that in mind, I had a question a little while ago about using an LDAP server to authenticate users for the FTP service, and it seemed like that would make a great subject for another custom FTP authentication provider blog post.

The steps in this blog will lead you through the steps to use managed code to create an FTP authentication provider that uses a server running Active Directory Lightweight Directory Services (AD LDS) that is located on your local network.

Note: I wrote and tested the steps in this blog using both Visual Studio 2010 and Visual Studio 2008; if you use an different version of Visual Studio, some of the version-specific steps may need to be changed.

In This Blog

Prerequisites

The following items are required to complete the procedures in this blog:

  1. The following version of IIS must be installed on your Windows computer, and the Internet Information Services (IIS) Manager must also be installed:
    • IIS 7.0 must be installed on Windows Server 2008
    • IIS 7.5 must be installed on Windows Server 2008 R2 or Windows 7
  2. The new FTP 7.5 service must be installed. To install FTP 7.5, follow the instructions in the following topic:
  3. You must have FTP publishing enabled for a site. To create a new FTP site, follow the instructions in the following topic:
  4. You must have an AD LDS server available on your local network. Note: See my How to Set Up an Active Directory Lightweight Directory Services (AD LDS) Server blog post for more information.

Note: To test this blog, I used AD LDS on Windows Server 2008; if you use a different LDAP server, you may need to change some of the LDAP syntax in the code samples. To get started using AD LDS, see the following topics:

I tested this blog by using the user objects from both the MS-User.LDF and MS-InetOrgPerson.LDF Lightweight Directory interchange Format (LDIF) files.

Important

To help improve the performance for authentication requests, the FTP service caches the credentials for successful logins for 15 minutes by default. This means that if you change the password in your AD LDS server, this change may not be reflected for the cache duration. To alleviate this, you can disable credential caching for the FTP service. To do so, use the following steps:

  1. Open a command prompt.
  2. Type the following commands: 
    cd /d "%SystemRoot%\System32\Inetsrv"
Appcmd.exe set config -section:system.ftpServer/caching /credentialsCache.enabled:"False" /commit:apphost
Net stop FTPSVC
Net start FTPSVC
  3. Close the command prompt.

Step 1: Set up the Project Environment

In this step, you will create a project in Visual Studio 2008 for the demo provider.

  1. Open Microsoft Visual Studio 2008.
  2. Click the File menu, then New, then Project.
  3. In the New Projectdialog box:
    • Choose Visual C# as the project type.
    • Choose Class Library as the template.
    • Type FtpLdapAuthentication as the name of the project.
    • Click OK.
  4. When the project opens, add a reference path to the FTP extensibility library:
    • Click Project, and then click FtpLdapAuthentication Properties.
    • Click the Reference Paths tab.
    • Enter the path to the FTP extensibility assembly for your version of Windows, where C: is your operating system drive.
      • For Windows Server 2008 and Windows Vista:
        • C:\Windows\assembly\GAC_MSIL\Microsoft.Web.FtpServer\7.5.0.0__31bf3856ad364e35
      • For 32-bit Windows 7 and Windows Server 2008 R2:
        • C:\Program Files\Reference Assemblies\Microsoft\IIS
      • For 64-bit Windows 7 and Windows Server 2008 R2:
        • C:\Program Files (x86)\Reference Assemblies\Microsoft\IIS
    • Click Add Folder.
  5. Add a strong name key to the project:
    • Click Project, and then click FtpLdapAuthentication Properties.
    • Click the Signing tab.
    • Check the Sign the assembly check box.
    • Choose <New...> from the strong key name drop-down box.
    • Enter FtpLdapAuthenticationKey for the key file name.
    • If desired, enter a password for the key file; otherwise, clear the Protect my key file with a password check box.
    • Click OK.
  6. Note: FTP 7.5 Extensibility does not support the .NET Framework 4.0; if you are using Visual Studio 2010, or you have changed your default framework version, you may need to change the framework version. To do so, use the following steps:
    • Click Project, and then click FtpLdapAuthentication Properties.
    • Click the Application tab.
    • Choose .NET Framework 3.5 in the Target framework drop-down menu.
    • Save, close, and re-open the project.
  7. Optional: You can add a custom build event to add the DLL automatically to the Global Assembly Cache (GAC) on your development computer:
    • Click Project, and then click FtpLdapAuthentication Properties.
    • Click the Build Events tab.
    • Enter the appropriate commands in the Post-build event command linedialog box, depending on your version of Visual Studio:
      • If you are using Visual Studio 2010:
        net stop ftpsvc
        call "%VS100COMNTOOLS%\vsvars32.bat">null
        gacutil.exe /if "$(TargetPath)"
        net start ftpsvc
      • If you are using Visual Studio 2008:
        net stop ftpsvc
        call "%VS90COMNTOOLS%\vsvars32.bat">null
        gacutil.exe /if "$(TargetPath)"
        net start ftpsvc
      Note: You need to be logged in as an administrator in order to restart the service and add the dll to the Global Assembly Cache.
  8. Save the project.

Step 2: Create the Extensibility Class

In this step, you will implement the authentication and role extensibility interfaces for the demo provider.

  1. Add the necessary references to the project:
    • Click Project, and then click Add Reference...
    • On the .NET tab, click Microsoft.Web.FtpServer.
    • Click OK.
    • Repeat the above steps to add the following references to the project:
      • System.Configuration
      • System.DirectoryServices
      • System.DirectoryServices.AccountManagement
  2. Add the code for the authentication class:
    • In Solution Explorer, double-click the Class1.cs file.
    • Remove the existing code.
    • Paste the following code into the editor: 
      using System;
using System.Collections.Specialized;
using System.Configuration.Provider;
using System.DirectoryServices;
using System.DirectoryServices.AccountManagement;
using Microsoft.Web.FtpServer;

public class FtpLdapAuthentication :
  BaseProvider,
  IFtpAuthenticationProvider,
  IFtpRoleProvider
{
  private static string _ldapServer = string.Empty;
  private static string _ldapPartition = string.Empty;
  private static string _ldapAdminUsername = string.Empty;
  private static string _ldapAdminPassword = string.Empty;

  // Override the default initialization method.
  protected override void Initialize(StringDictionary config)
  {
    // Retrieve the provider settings from configuration.
    _ldapServer = config["ldapServer"];
    _ldapPartition = config["ldapPartition"];
    _ldapAdminUsername = config["ldapAdminUsername"];
    _ldapAdminPassword = config["ldapAdminPassword"];

    // Test for the LDAP server name (Required).
    if (string.IsNullOrEmpty(_ldapServer) || string.IsNullOrEmpty(_ldapPartition))
    {
      throw new ArgumentException(
        "Missing LDAP server values in configuration.");
    }
  }

  public bool AuthenticateUser(
    string sessionId,
    string siteName,
    string userName,
    string userPassword,
    out string canonicalUserName)
  {
    canonicalUserName = userName;
    // Attempt to look up the user and password.
    return LookupUser(true, userName, string.Empty, userPassword);
  }

  public bool IsUserInRole(
    string sessionId,
    string siteName,
    string userName,
    string userRole)
  {
    // Attempt to look up the user and role.
    return LookupUser(false, userName, userRole, string.Empty);
  }

  private static bool LookupUser(
    bool isUserLookup,
    string userName,
    string userRole,
    string userPassword)
  {
    PrincipalContext _ldapPrincipalContext = null;
    DirectoryEntry _ldapDirectoryEntry = null;

    try
    {
      // Create the context object using the LDAP connection information.
      _ldapPrincipalContext = new PrincipalContext(
        ContextType.ApplicationDirectory,
        _ldapServer,

        _ldapPartition,
        ContextOptions.SimpleBind,
        _ldapAdminUsername,
        _ldapAdminPassword);

      // Test for LDAP credentials.
      if (string.IsNullOrEmpty(_ldapAdminUsername) || string.IsNullOrEmpty(_ldapAdminPassword))
      {
        // If LDAP credentials do not exist, attempt to create an unauthenticated directory entry object.
        _ldapDirectoryEntry = new DirectoryEntry("LDAP://" + _ldapServer + "/" + _ldapPartition);
      }
      else
      {
        // If LDAP credentials exist, attempt to create an authenticated directory entry object.
        _ldapDirectoryEntry = new DirectoryEntry("LDAP://" + _ldapServer + "/" + _ldapPartition,
          _ldapAdminUsername, _ldapAdminPassword, AuthenticationTypes.Secure);
      }

      // Create a DirectorySearcher object from the cached DirectoryEntry object.
      DirectorySearcher userSearcher = new DirectorySearcher(_ldapDirectoryEntry);
      // Specify the the directory searcher to filter by the user name.
      userSearcher.Filter = String.Format("(&(objectClass=user)(cn={0}))", userName);
      // Specify the search scope.
      userSearcher.SearchScope = SearchScope.Subtree;
      // Specify the directory properties to load.
      userSearcher.PropertiesToLoad.Add("distinguishedName");
      // Specify the search timeout.
      userSearcher.ServerTimeLimit = new TimeSpan(0, 1, 0);
      // Retrieve a single search result.
      SearchResult userResult = userSearcher.FindOne();
      // Test if no result was found.
      if (userResult == null)
      {
        // Return false if no matching user was found.
        return false;
      }
      else
      {
        if (isUserLookup == true)
        {
          try
          {
            // Attempt to validate credentials using the username and password.
            return _ldapPrincipalContext.ValidateCredentials(userName, userPassword, ContextOptions.SimpleBind);
          }
          catch (Exception ex)
          {
            // Throw an exception if an error occurs.
            throw new ProviderException(ex.Message);
          }
        }
        else
        {
          // Retrieve the distinguishedName for the user account.
          string distinguishedName = userResult.Properties["distinguishedName"][0].ToString();

          // Create a DirectorySearcher object from the cached DirectoryEntry object.
          DirectorySearcher groupSearcher = new DirectorySearcher(_ldapDirectoryEntry);
          // Specify the the directory searcher to filter by the group/role name.
          groupSearcher.Filter = String.Format("(&(objectClass=group)(cn={0}))", userRole);
          // Specify the search scope.
          groupSearcher.SearchScope = SearchScope.Subtree;
          // Specify the directory properties to load.
          groupSearcher.PropertiesToLoad.Add("member");
          // Specify the search timeout.
          groupSearcher.ServerTimeLimit = new TimeSpan(0, 1, 0);
          // Retrieve a single search result.
          SearchResult groupResult = groupSearcher.FindOne();

          // Loop through the member collection.
          for (int i = 0; i < groupResult.Properties["member"].Count; ++i)
          {
            string member = groupResult.Properties["member"][i].ToString();
            // Test if the current member contains the user's distinguished name.
            if (member.IndexOf(distinguishedName, StringComparison.OrdinalIgnoreCase) > -1)
            {
              // Return true (role lookup succeeded) if the user is found.
              return true;
            }
          }
          // Return false (role lookup failed) if the user is not found for the role.
          return false;
        }
      }
    }
    catch (Exception ex)
    {
      // Throw an exception if an error occurs.
      throw new ProviderException(ex.Message);
    }
  }
}
  3. Save and compile the project.

Note: If you did not use the optional steps to register the assemblies in the GAC, you will need to manually copy the assemblies to your IIS 7 computer and add the assemblies to the GAC using the Gacutil.exe tool. For more information, see the following topic on the Microsoft MSDN Web site:

Global Assembly Cache Tool (Gacutil.exe)

Step 3: Add the Demo Provider to FTP

In this step, you will add your provider to the list of providers for your FTP service, configure your provider for your LDAP server, and enable your provider to authenticate users for an FTP site.

Adding your Provider to FTP

  1. Determine the assembly information for your extensibility provider:
    • In Windows Explorer, open your "C:\Windows\assembly" path, where C: is your operating system drive.
    • Locate the FtpLdapAuthentication assembly.
    • Right-click the assembly, and then click Properties.
    • Copy the Culture value; for example: Neutral.
    • Copy the Version number; for example: 1.0.0.0.
    • Copy the Public Key Token value; for example: 426f62526f636b73.
    • Click Cancel.
  2. Add the extensibility provider to the global list of FTP authentication providers:
    • Open the Internet Information Services (IIS) Manager.
    • Click your computer name in the Connections pane.
    • Double-click FTP Authentication in the main window.
    • Click Custom Providers... in the Actions pane.
    • Click Register.
    • Enter FtpLdapAuthentication for the provider Name.
    • Click Managed Provider (.NET).
    • Enter the assembly information for the extensibility provider using the information that you copied earlier. For example:
      FtpLdapAuthentication,FtpLdapAuthentication,version=1.0.0.0,Culture=neutral,PublicKeyToken=426f62526f636b73
    • Click OK.
    • Clear the FtpLdapAuthentication check box in the providers list.
    • Click OK.

Configuring your Provider's Settings

  1. Determine the connection information for your LDAP server; there are four pieces of information that you will need to know in order to configure the extensibility provider to talk to your LDAP server:
    • Server Name and TCP/IP Port: This is the name (or IP address) of the server that is hosting your LDAP service; the port is usually 389. These will be added to your provider using the "SERVERNAME:PORT" syntax.
    • LDAP Partition: This is the LDAP path within your LDAP service to your data, for example: "CN=ServerName,DC=DomainName,DC=DomainExtension."
    • LDAP Username: This is a username that has access to your LDAP server; this is not the name of an account that you will use for FTP access, and it does not have to be a Windows account.
    • LDAP Password: This is the password that is associated with the LDAP username.
  2. Using the information from the previous steps, configure the options for the provider:
    • At the moment there is no user interface that enables you to add properties for a custom authentication module, so you will have to use the following command line. You will need to update the highlighted areas with the information from the previous steps and the information for your LDAP server:
      cd %SystemRoot%\System32\Inetsrv

      appcmd.exe set config -section:system.ftpServer/providerDefinitions /+"activation.[name='FtpLdapAuthentication']" /commit:apphost

      appcmd.exe set config -section:system.ftpServer/providerDefinitions /+"activation.[name='FtpLdapAuthentication'].[key='ldapServer',value='MYSERVER:389']" /commit:apphost

      appcmd.exe set config -section:system.ftpServer/providerDefinitions /+"activation.[name='FtpLdapAuthentication'].[key='ldapPartition',value='CN=MyServer,DC=MyDomain,DC=local']" /commit:apphost

      appcmd.exe set config -section:system.ftpServer/providerDefinitions /+"activation.[name='FtpLdapAuthentication'].[key='ldapAdminUsername',encryptedValue='MyAdmin']" /commit:apphost

      appcmd.exe set config -section:system.ftpServer/providerDefinitions /+"activation.[name='FtpLdapAuthentication'].[key='ldapAdminPassword',encryptedValue='MyPassword1']" /commit:apphost
    • Note: The highlighted areas are the values for the ldapServer, ldapPartition, ldapAdminUsername, and ldapAdminPassword settings, which configure your network environment for your LDAP server.

Enabling your Provider for an FTP site

  1. Add the custom authentication provider for an FTP site:
    • Open an FTP site in the Internet Information Services (IIS) Manager.
    • Double-click FTP Authentication in the main window.
    • Click Custom Providers... in the Actions pane.
    • Check FtpLdapAuthentication in the providers list.
    • Click OK.
  2. Add an authorization rule for the authentication provider:
    • Double-click FTP Authorization Rules in the main window.
    • Click Add Allow Rule... in the Actions pane.
    • You can add either of the following authorization rules:
      • For a specific user:
        • Select Specified users for the access option.
        • Enter a user name that you created in your AD LDS partition.
      • For a role or group:
        • Select Specified roles or user groups for the access option.
        • Enter the role or group name that you created in your AD LDS partition.
      • Select Read and/or Write for the Permissions option.
    • Click OK.

Summary

In this blog I showed you how to:

  • Create a project in Visual Studio 2010 or Visual Studio 2008 for a custom FTP authentication provider.
  • Implement the extensibility interface for custom FTP authentication.
  • Add a custom authentication provider to your FTP service.

When users connect to your FTP site, the FTP service will attempt to authenticate users from your LDAP server by using your custom authentication provider.

Additional Information

The PrincipalContext.ValidateCredentials() method will validate the user name in the userName parameter with the value of the userPrincipalName attribute of the user object in AD LDS. Because of this, the userPrincipalName attribute for a user object is expected to match the name of the user account that an FTP client will use to log in, which will should be the same value as the cn attribute for the user object. Therefore, when you create a user object in AD LDS, you will need to set the corresponding userPrincipalName attribute for the user object. In addition, when you create a user object in AD LDS, the msDS-UserAccountDisabled attribute is set to TRUE by default, so you will need to change the value of that attribute to FALSE before you attempt to log in.

For more information, see my follow-up blog that is titled FTP and LDAP - Part 2: How to Set Up an Active Directory Lightweight Directory Services (AD LDS) Server.

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