ASP .NET authentication against Active Directory and Roles via ASP.NET role provider

If you work on .NET 3.5 or newer, you can use the System.DirectoryServices.AccountManagement namespace and easily verify your credentials:

// create a "principal context" - e.g. your domain (could be machine, too)
using(PrincipalContext pc = new PrincipalContext(ContextType.Domain, "YOURDOMAIN"))
{
    // validate the credentials
    bool isValid = pc.ValidateCredentials("myuser", "mypassword");
}

It's simple, it's reliable, it's 100% C# managed code on your end - what more can you ask for? :-)

Read all about it here:

• Managing Directory Security Principals in the .NET Framework 3.5
• MSDN docs on System.DirectoryServices.AccountManagement

Update:

As outlined in this other SO question (and its answers), there is an issue with this call possibly returning True for old passwords of a user. Just be aware of this behavior and don't be too surprised if this happens :-) (thanks to @MikeGledhill for pointing this out!)

Using AD for your authentication is a great idea, since you need to add everyone there anyway, and for intranet users there's no need for an extra login.

You're correct that ASP.NET allows you to use a Provider which will allow you to authenticate against AD, although there's nothing included to give you group membership support (although it's quite trivial to implement if you want to, I can provide a sample).

The real issue here is if you want to use AD groups to define permissions within each app, yes?

If so then you do have the option of creating your own RoleProvider for ASP.NET that can also be used by WinForms and WPF apps via ApplicationServices. This RoleProvider could link the ID of the user in AD to groups/roles per app which you can store in your own custom database, which also allows each app to allow administration of these roles without requiring these admins to have extra privileges in AD.

If you want you can also have an override and combine app roles with AD groups, so if they're in some global "Admin" group in AD they get full permission in the App regardless of App role membership. Conversely if they have either a group or property in AD to say they've been fired you could ignore all App role membership and restrict all access (since HR probably wouldn't remove them from each and every app, assuming they even know about them all!).

Sample code added as requested:

NOTE: based on this original work http://www.codeproject.com/Articles/28546/Active-Directory-Roles-Provider

For your ActiveDirectoryMembershipProvider you only need to implement the ValidateUser method, although you could implement more if you desired, the new AccountManagement namespace makes this trivial:

// assumes: using System.DirectoryServices.AccountManagement;
public override bool ValidateUser( string username, string password )
{
  bool result = false;

  try
  {
    using( var context = 
        new PrincipalContext( ContextType.Domain, "yourDomainName" ) )
    {
      result = context.ValidateCredentials( username, password );
    }
  }
  catch( Exception ex )
  {
    // TODO: log exception
  }

  return result;
}

For your role provider it's a little bit more work, there's some key issues we discovered while searching google such as groups you want to exclude, users you want to exclude etc.

It's probably worth a full blog post, but this should help you get started, it's caching lookups in Session variables, just as a sample of how you could improve performance (since a full Cache sample would be too long).

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Configuration.Provider;
using System.Diagnostics;
using System.DirectoryServices;
using System.DirectoryServices.AccountManagement;
using System.Linq;
using System.Web;
using System.Web.Hosting;
using System.Web.Security;

namespace MyApp.Security
{
    public sealed class ActiveDirectoryRoleProvider : RoleProvider
    {
        private const string AD_FILTER = "(&(objectCategory=group)(|(groupType=-2147483646)(groupType=-2147483644)(groupType=-2147483640)))";
        private const string AD_FIELD = "samAccountName";

        private string _activeDirectoryConnectionString;
        private string _domain;

        // Retrieve Group Mode
        // "Additive" indicates that only the groups specified in groupsToUse will be used
        // "Subtractive" indicates that all Active Directory groups will be used except those specified in groupsToIgnore
        // "Additive" is somewhat more secure, but requires more maintenance when groups change
        private bool _isAdditiveGroupMode;

        private List<string> _groupsToUse;
        private List<string> _groupsToIgnore;
        private List<string> _usersToIgnore;

        #region Ignore Lists

        // IMPORTANT - DEFAULT LIST OF ACTIVE DIRECTORY USERS TO "IGNORE"
        //             DO NOT REMOVE ANY OF THESE UNLESS YOU FULLY UNDERSTAND THE SECURITY IMPLICATIONS
        //             VERYIFY THAT ALL CRITICAL USERS ARE IGNORED DURING TESTING
        private String[] _DefaultUsersToIgnore = new String[]
        {
            "Administrator", "TsInternetUser", "Guest", "krbtgt", "Replicate", "SERVICE", "SMSService"
        };

        // IMPORTANT - DEFAULT LIST OF ACTIVE DIRECTORY DOMAIN GROUPS TO "IGNORE"
        //             PREVENTS ENUMERATION OF CRITICAL DOMAIN GROUP MEMBERSHIP
        //             DO NOT REMOVE ANY OF THESE UNLESS YOU FULLY UNDERSTAND THE SECURITY IMPLICATIONS
        //             VERIFY THAT ALL CRITICAL GROUPS ARE IGNORED DURING TESTING BY CALLING GetAllRoles MANUALLY
        private String[] _defaultGroupsToIgnore = new String[]
            {
                "Domain Guests", "Domain Computers", "Group Policy Creator Owners", "Guests", "Users",
                "Domain Users", "Pre-Windows 2000 Compatible Access", "Exchange Domain Servers", "Schema Admins",
                "Enterprise Admins", "Domain Admins", "Cert Publishers", "Backup Operators", "Account Operators",
                "Server Operators", "Print Operators", "Replicator", "Domain Controllers", "WINS Users",
                "DnsAdmins", "DnsUpdateProxy", "DHCP Users", "DHCP Administrators", "Exchange Services",
                "Exchange Enterprise Servers", "Remote Desktop Users", "Network Configuration Operators",
                "Incoming Forest Trust Builders", "Performance Monitor Users", "Performance Log Users",
                "Windows Authorization Access Group", "Terminal Server License Servers", "Distributed COM Users",
                "Administrators", "Everybody", "RAS and IAS Servers", "MTS Trusted Impersonators",
                "MTS Impersonators", "Everyone", "LOCAL", "Authenticated Users"
            };
        #endregion

        /// <summary>
        /// Initializes a new instance of the ADRoleProvider class.
        /// </summary>
        public ActiveDirectoryRoleProvider()
        {
            _groupsToUse = new List<string>();
            _groupsToIgnore = new List<string>();
            _usersToIgnore = new List<string>();
        }

        public override String ApplicationName { get; set; }

        /// <summary>
        /// Initialize ADRoleProvider with config values
        /// </summary>
        /// <param name="name"></param>
        /// <param name="config"></param>
        public override void Initialize( String name, NameValueCollection config )
        {
            if ( config == null )
                throw new ArgumentNullException( "config" );

            if ( String.IsNullOrEmpty( name ) )
                name = "ADRoleProvider";

            if ( String.IsNullOrEmpty( config[ "description" ] ) )
            {
                config.Remove( "description" );
                config.Add( "description", "Active Directory Role Provider" );
            }

            // Initialize the abstract base class.
            base.Initialize( name, config );

            _domain = ReadConfig( config, "domain" );
            _isAdditiveGroupMode = ( ReadConfig( config, "groupMode" ) == "Additive" );
            _activeDirectoryConnectionString = ReadConfig( config, "connectionString" );

            DetermineApplicationName( config );
            PopulateLists( config );
        }

        private string ReadConfig( NameValueCollection config, string key )
        {
            if ( config.AllKeys.Any( k => k == key ) )
                return config[ key ];

            throw new ProviderException( "Configuration value required for key: " + key );
        }

        private void DetermineApplicationName( NameValueCollection config )
        {
            // Retrieve Application Name
            ApplicationName = config[ "applicationName" ];
            if ( String.IsNullOrEmpty( ApplicationName ) )
            {
                try
                {
                    string app =
                        HostingEnvironment.ApplicationVirtualPath ??
                        Process.GetCurrentProcess().MainModule.ModuleName.Split( '.' ).FirstOrDefault();

                    ApplicationName = app != "" ? app : "/";
                }
                catch
                {
                    ApplicationName = "/";
                }
            }

            if ( ApplicationName.Length > 256 )
                throw new ProviderException( "The application name is too long." );
        }

        private void PopulateLists( NameValueCollection config )
        {
            // If Additive group mode, populate GroupsToUse with specified AD groups
            if ( _isAdditiveGroupMode && !String.IsNullOrEmpty( config[ "groupsToUse" ] ) )
                _groupsToUse.AddRange(
                    config[ "groupsToUse" ].Split( ',' ).Select( group => group.Trim() )
                );

            // Populate GroupsToIgnore List<string> with AD groups that should be ignored for roles purposes
            _groupsToIgnore.AddRange(
                _defaultGroupsToIgnore.Select( group => group.Trim() )
            );

            _groupsToIgnore.AddRange(
                ( config[ "groupsToIgnore" ] ?? "" ).Split( ',' ).Select( group => group.Trim() )
            );

            // Populate UsersToIgnore ArrayList with AD users that should be ignored for roles purposes
            string usersToIgnore = config[ "usersToIgnore" ] ?? "";
            _usersToIgnore.AddRange(
                _DefaultUsersToIgnore
                    .Select( value => value.Trim() )
                    .Union(
                        usersToIgnore
                            .Split( new[] { "," }, StringSplitOptions.RemoveEmptyEntries )
                            .Select( value => value.Trim() )
                    )
            );
        }

        private void RecurseGroup( PrincipalContext context, string group, List<string> groups )
        {
            var principal = GroupPrincipal.FindByIdentity( context, IdentityType.SamAccountName, group );

            if ( principal == null )
                return;

            List<string> res =
                principal
                    .GetGroups()
                    .ToList()
                    .Select( grp => grp.Name )
                    .ToList();

            groups.AddRange( res.Except( groups ) );
            foreach ( var item in res )
                RecurseGroup( context, item, groups );
        }

        /// <summary>
        /// Retrieve listing of all roles to which a specified user belongs.
        /// </summary>
        /// <param name="username"></param>
        /// <returns>String array of roles</returns>
        public override string[] GetRolesForUser( string username )
        {
            string sessionKey = "groupsForUser:" + username;

            if ( HttpContext.Current != null &&
                 HttpContext.Current.Session != null &&
                 HttpContext.Current.Session[ sessionKey ] != null
            )
                return ( (List<string>) ( HttpContext.Current.Session[ sessionKey ] ) ).ToArray();

            using ( PrincipalContext context = new PrincipalContext( ContextType.Domain, _domain ) )
            {
                try
                {
                    // add the users groups to the result
                    var groupList =
                        UserPrincipal
                            .FindByIdentity( context, IdentityType.SamAccountName, username )
                            .GetGroups()
                            .Select( group => group.Name )
                            .ToList();

                    // add each groups sub groups into the groupList
                    foreach ( var group in new List<string>( groupList ) )
                        RecurseGroup( context, group, groupList );

                    groupList = groupList.Except( _groupsToIgnore ).ToList();

                    if ( _isAdditiveGroupMode )
                        groupList = groupList.Join( _groupsToUse, r => r, g => g, ( r, g ) => r ).ToList();

                    if ( HttpContext.Current != null )
                        HttpContext.Current.Session[ sessionKey ] = groupList;

                    return groupList.ToArray();
                }
                catch ( Exception ex )
                {
                    // TODO: LogError( "Unable to query Active Directory.", ex );
                    return new[] { "" };
                }
            }
        }

        /// <summary>
        /// Retrieve listing of all users in a specified role.
        /// </summary>
        /// <param name="rolename">String array of users</param>
        /// <returns></returns>
        public override string[] GetUsersInRole( String rolename )
        {
            if ( !RoleExists( rolename ) )
                throw new ProviderException( String.Format( "The role '{0}' was not found.", rolename ) );

            using ( PrincipalContext context = new PrincipalContext( ContextType.Domain, _domain ) )
            {
                try
                {
                    GroupPrincipal p = GroupPrincipal.FindByIdentity( context, IdentityType.SamAccountName, rolename );

                    return (

                        from user in p.GetMembers( true )
                        where !_usersToIgnore.Contains( user.SamAccountName )
                        select user.SamAccountName

                    ).ToArray();
                }
                catch ( Exception ex )
                {
                    // TODO: LogError( "Unable to query Active Directory.", ex );
                    return new[] { "" };
                }
            }
        }

        /// <summary>
        /// Determine if a specified user is in a specified role.
        /// </summary>
        /// <param name="username"></param>
        /// <param name="rolename"></param>
        /// <returns>Boolean indicating membership</returns>
        public override bool IsUserInRole( string username, string rolename )
        {
            return GetUsersInRole( rolename ).Any( user => user == username );
        }

        /// <summary>
        /// Retrieve listing of all roles.
        /// </summary>
        /// <returns>String array of roles</returns>
        public override string[] GetAllRoles()
        {
            string[] roles = ADSearch( _activeDirectoryConnectionString, AD_FILTER, AD_FIELD );

            return (

                from role in roles.Except( _groupsToIgnore )
                where !_isAdditiveGroupMode || _groupsToUse.Contains( role )
                select role

            ).ToArray();
        }

        /// <summary>
        /// Determine if given role exists
        /// </summary>
        /// <param name="rolename">Role to check</param>
        /// <returns>Boolean indicating existence of role</returns>
        public override bool RoleExists( string rolename )
        {
            return GetAllRoles().Any( role => role == rolename );
        }

        /// <summary>
        /// Return sorted list of usernames like usernameToMatch in rolename
        /// </summary>
        /// <param name="rolename">Role to check</param>
        /// <param name="usernameToMatch">Partial username to check</param>
        /// <returns></returns>
        public override string[] FindUsersInRole( string rolename, string usernameToMatch )
        {
            if ( !RoleExists( rolename ) )
                throw new ProviderException( String.Format( "The role '{0}' was not found.", rolename ) );

            return (
                from user in GetUsersInRole( rolename )
                where user.ToLower().Contains( usernameToMatch.ToLower() )
                select user

            ).ToArray();
        }

        #region Non Supported Base Class Functions

        /// <summary>
        /// AddUsersToRoles not supported.  For security and management purposes, ADRoleProvider only supports read operations against Active Direcory. 
        /// </summary>
        public override void AddUsersToRoles( string[] usernames, string[] rolenames )
        {
            throw new NotSupportedException( "Unable to add users to roles.  For security and management purposes, ADRoleProvider only supports read operations against Active Direcory." );
        }

        /// <summary>
        /// CreateRole not supported.  For security and management purposes, ADRoleProvider only supports read operations against Active Direcory. 
        /// </summary>
        public override void CreateRole( string rolename )
        {
            throw new NotSupportedException( "Unable to create new role.  For security and management purposes, ADRoleProvider only supports read operations against Active Direcory." );
        }

        /// <summary>
        /// DeleteRole not supported.  For security and management purposes, ADRoleProvider only supports read operations against Active Direcory. 
        /// </summary>
        public override bool DeleteRole( string rolename, bool throwOnPopulatedRole )
        {
            throw new NotSupportedException( "Unable to delete role.  For security and management purposes, ADRoleProvider only supports read operations against Active Direcory." );
        }

        /// <summary>
        /// RemoveUsersFromRoles not supported.  For security and management purposes, ADRoleProvider only supports read operations against Active Direcory. 
        /// </summary>
        public override void RemoveUsersFromRoles( string[] usernames, string[] rolenames )
        {
            throw new NotSupportedException( "Unable to remove users from roles.  For security and management purposes, ADRoleProvider only supports read operations against Active Direcory." );
        }
        #endregion

        /// <summary>
        /// Performs an extremely constrained query against Active Directory.  Requests only a single value from
        /// AD based upon the filtering parameter to minimize performance hit from large queries.
        /// </summary>
        /// <param name="ConnectionString">Active Directory Connection String</param>
        /// <param name="filter">LDAP format search filter</param>
        /// <param name="field">AD field to return</param>
        /// <returns>String array containing values specified by 'field' parameter</returns>
        private String[] ADSearch( String ConnectionString, String filter, String field )
        {
            DirectorySearcher searcher = new DirectorySearcher
            {
                SearchRoot = new DirectoryEntry( ConnectionString ),
                Filter = filter,
                PageSize = 500
            };
            searcher.PropertiesToLoad.Clear();
            searcher.PropertiesToLoad.Add( field );

            try
            {
                using ( SearchResultCollection results = searcher.FindAll() )
                {
                    List<string> r = new List<string>();
                    foreach ( SearchResult searchResult in results )
                    {
                        var prop = searchResult.Properties[ field ];
                        for ( int index = 0; index < prop.Count; index++ )
                            r.Add( prop[ index ].ToString() );
                    }

                    return r.Count > 0 ? r.ToArray() : new string[ 0 ];
                }
            }
            catch ( Exception ex )
            {
                throw new ProviderException( "Unable to query Active Directory.", ex );
            }
        }
    }
}

A sample config sub-section entry for this would be as follows:

<roleManager enabled="true" defaultProvider="ActiveDirectory">
  <providers>
    <clear/>
    <add
        applicationName="MyApp" name="ActiveDirectory"
        type="MyApp.Security.ActiveDirectoryRoleProvider"
        domain="mydomain" groupMode="" connectionString="LDAP://myDirectoryServer.local/dc=mydomain,dc=local"
    />
  </providers>
</roleManager>

Whew, that's a lot of code!

PS: Core parts of the Role Provider above are based on another person's work, I don't have the link handy but we found it via Google, so partial credit to that person for the original. We modified it heavily to use LINQ and to get rid of the need for a database for caching.