Implement Active Directory Role Provider

I've been using the ActiveDirectoryMembershipProvider to allow my users to login to a custom ASP.Net site with their AD credentials and it is pretty straight forward. Recently I needed to add more granularity to who can view various parts of the site. I wanted to take advantage of our existing AD groups so I assumed there would be something like an ActiveDirectoryRoleProvider as well. After a little searching, it became clear that wasn't the case, so I decided to roll my own.
Creating a custom role provider is pretty easy, all you have to do is create a new class and inherit RoleProvider:

public class ActiveDirectoryRoleProvider : RoleProvider
{}

You will have to create stubs for all the inherited members. We only need to implement a couple of them to get basic role membership checking. We need to get our AD configuration information out of the Web.Config values, so we'll create a few properties and override the Initialize method:

private string ConnectionStringName { get; set; }
private string ConnectionUsername { get; set; }
private string ConnectionPassword { get; set; }
private string AttributeMapUsername { get; set; }

public override void Initialize(string name, NameValueCollection config)
{
    ConnectionStringName = config["connectionStringName"];
    ConnectionUsername = config["connectionUsername"];
    ConnectionPassword = config["connectionPassword"];
    AttributeMapUsername = config["attributeMapUsername"];
    
    base.Initialize(name, config);
}

Now we'll override GetRolesForUser which is the bulk of our implementation. We use the DirectorySearcher class in System.DirectoryServices to query AD for the passed username. We then pull the memberOf property from that user and extract the CN component for each entry as the role:

public override string[] GetRolesForUser(string username)
{
    var allRoles = new List<string>();

    var root = new DirectoryEntry(WebConfigurationManager.ConnectionStrings[ConnectionStringName].ConnectionString, ConnectionUsername, ConnectionPassword);

    var searcher = new DirectorySearcher(root, string.Format(CultureInfo.InvariantCulture, "(&(objectClass=user)({0}={1}))", AttributeMapUsername, username));
    searcher.PropertiesToLoad.Add("memberOf");

    SearchResult result = searcher.FindOne();

    if (result != null && !string.IsNullOrEmpty(result.Path))
    {
        DirectoryEntry user = result.GetDirectoryEntry();

        PropertyValueCollection groups = user.Properties["memberOf"];

        foreach (string path in groups)
        {
            string[] parts = path.Split(',');

            if (parts.Length > 0)
            {
                foreach (string part in parts)
                {
                    string[] p = part.Split('=');

                    if (p[0].Equals("cn", StringComparison.OrdinalIgnoreCase))
                    {
                        allRoles.Add(p[1]);
                    }
                }
            }
        }
    }

    return allRoles.ToArray();
}

And finally we need to override IsUserInRole so we can easily check for role membership in code:

public override bool IsUserInRole(string username, string roleName)
{
    string[] roles = GetRolesForUser(username);

    foreach (string role in roles)
    {
        if (role.Equals(roleName, StringComparison.OrdinalIgnoreCase))
        {
            return true;
        }
    }

    return false;
}

Here's the the full code (minus the unimplemented inherited methods):

public class ActiveDirectoryRoleProvider : RoleProvider
{
    private string ConnectionStringName { get; set; }
    private string ConnectionUsername { get; set; }
    private string ConnectionPassword { get; set; }
    private string AttributeMapUsername { get; set; }

    public override void Initialize(string name, NameValueCollection config)
    {
        ConnectionStringName = config["connectionStringName"];
        ConnectionUsername = config["connectionUsername"];
        ConnectionPassword = config["connectionPassword"];
        AttributeMapUsername = config["attributeMapUsername"];

        base.Initialize(name, config);
    }

    public override bool IsUserInRole(string username, string roleName)
    {
        string[] roles = GetRolesForUser(username);

        foreach (string role in roles)
        {
            if (role.Equals(roleName, StringComparison.OrdinalIgnoreCase))
            {
                return true;
            }
        }

        return false;
    }

    public override string[] GetRolesForUser(string username)
    {
        var allRoles = new List<string>();

        var root = new DirectoryEntry(WebConfigurationManager.ConnectionStrings[ConnectionStringName].ConnectionString, ConnectionUsername, ConnectionPassword);

        var searcher = new DirectorySearcher(root, string.Format(CultureInfo.InvariantCulture, "(&(objectClass=user)({0}={1}))", AttributeMapUsername, username));
        searcher.PropertiesToLoad.Add("memberOf");

        SearchResult result = searcher.FindOne();

        if (result != null && !string.IsNullOrEmpty(result.Path))
        {
            DirectoryEntry user = result.GetDirectoryEntry();

            PropertyValueCollection groups = user.Properties["memberOf"];

            foreach (string path in groups)
            {
                string[] parts = path.Split(',');

                if (parts.Length > 0)
                {
                    foreach (string part in parts)
                    {
                        string[] p = part.Split('=');

                        if (p[0].Equals("cn", StringComparison.OrdinalIgnoreCase))
                        {
                            allRoles.Add(p[1]);
                        }
                    }
                }
            }
        }

        return allRoles.ToArray();
    }
}

Add the role provider to your Web.Config:

<system.web>
    <roleManager enabled="true" defaultProvider="ADRoleProvider" cacheRolesInCookie="true" cookieName=".ASPXROLES" cookiePath="/"
                 cookieTimeout="30" cookieRequireSSL="false" cookieSlidingExpiration="true" createPersistentCookie="false" cookieProtection="All">
        <providers>
            <clear />
            <add name="ActiveDirectoryRoleProvider" connectionStringName="ADConnectionString" connectionUsername="username"
                 connectionPassword="password" attributeMapUsername="sAMAccountName" type="ActiveDirectoryRoleProvider" />
        </providers>
    </roleManager>
</system.web>

You can then check the roles of your user in code like so:

Roles.IsUserInRole("My Group")

Or control access to entire directories via the Web.Config:

<location path="RestrictedSubDirectory">
    <system.web>
        <authorization>
            <allow roles="My Group"/>
            <deny users="*" />
        </authorization>
    </system.web>
</location>