C#: Validate a username and password from LDAP

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ASP.NET

We need to add System.DirectoryServices DLL reference in our project. In packages.config file, we can add the below package or install it using NuGet.

<packages>
  <package id="System.DirectoryServices" version="4.7.0" targetFramework="net461" />
</packages>

Here is the manager class, Validate(string userId, string password) method will validate things from LDAP server.

/*
 * Links:
 * https://www.nuget.org/packages/System.DirectoryServices/
 */
using System.DirectoryServices;

namespace DotNet
{
    /// <summary>
    /// Ldap related contracts
    /// </summary>
    public interface ILdapValidator
    {
        /// <summary>
        /// Check if user in Ldap 
        /// </summary>
        /// <param name="userId">Ldap user name without domain name</param>
        /// <param name="password">Ldap passsword</param>
        bool Validate(string userId, string password);
    }

    /// <summary>
    /// Ldap related tasks manager
    /// </summary>
    public class LdapManager : ILdapValidator
    {
        /// <summary>
        /// Domain name from config file
        /// </summary>
        public readonly string DomainName;
        /// <summary>
        /// Port name form config file, default 389
        /// </summary>
        public readonly int PortNumber;

        public LdapManager(string domainName, int port = 389)
        {
            DomainName = domainName;
            PortNumber = port;
        }

        /// <summary>
        /// Check if user in Ldap 
        /// </summary>
        /// <param name="userId">Ldap user name without domain name</param>
        /// <param name="password">Ldap passsword</param>
        public bool Validate(string userId, string password)
        {
            try
            {
                string path = LdapPath();
                string username = UserFullId(userId);
                DirectoryEntry de = new DirectoryEntry
                         (path, username, password, AuthenticationTypes.Secure);
                DirectorySearcher ds = new DirectorySearcher(de);
                ds.FindOne();
                return true;
            }
            catch (DirectoryServicesCOMException ex)
            {
                return false;
            }
        }

        /// <summary>
        /// User full id 
        /// </summary>
        /// <param name="userId">User name</param>
        /// <returns>userName@domain</returns>
        public string UserFullId(string userId)
        {
            string value = string.Format(@"{0}@{1}", userId, DomainName);
            return value;
        }

        /// <summary>
        /// Get Ldap path from domain and port
        /// </summary>
        /// <returns></returns>
        public string LdapPath()
        {
            string value = string.Format(@"LDAP://{0}:{1}", DomainName, PortNumber);
            return value;
        }
    }
}

Here, we are using the LDAP manager class to validate username and password:

string domain = "LdapdomainNameOrIp.com";
int port = 389;
string user = "user.name";
string password = "password@123";
bool isValied = new LdapManager(domain, port).Validate(user, password);

ASP.NET Core

We need to add Novell.Directory.Ldap DLL reference in our project. In .csproj file, we can add the below package or install it from NuGet.

<ItemGroup>
  <PackageReference Include="Novell.Directory.Ldap.NETStandard" Version="2.3.8" />
</ItemGroup>

Here is the manager class, Validate(string userId, string password) method will validate things from LDAP server.

/*
 * Links:
 * https://www.nuget.org/packages/Novell.Directory.Ldap.NETStandard/2.3.8
*/

using Novell.Directory.Ldap;
using System;

namespace DotNetCore
{
    /// <summary>
    /// Ldap related contracts
    /// </summary>
    public interface ILdapValidator
    {
        /// <summary>
        /// Check if user in Ldap 
        /// </summary>
        /// <param name="userId">Ldap user name without domain name</param>
        /// <param name="password">Ldap passsword</param>
        bool Validate(string userId, string password);
    }

    /// <summary>
    /// Ldap related tasks manager
    /// </summary>
    public class LdapManager : ILdapValidator
    {
        /// <summary>
        /// Domain name from config file
        /// </summary>
        public readonly string DomainName;
        /// <summary>
        /// Port name form config file, default 389
        /// </summary>
        public readonly int PortNumber;

        public LdapManager(string domainName, int port = 389)
        {
            DomainName = domainName;
            PortNumber = port;      /*LdapConnection.DEFAULT_PORT*/
        }

        /// <summary>
        /// Check if user in Ldap 
        /// </summary>
        /// <param name="userId">Ldap user name without domain name</param>
        /// <param name="password">Ldap passsword</param>
        public bool Validate(string userId, string password)
        {
            try
            {
                string username = UserFullId(userId);  
                using (var connection = new LdapConnection { SecureSocketLayer = false })
                {
                    connection.Connect(DomainName, PortNumber);
                    connection.Bind(username, password);
                    return connection.Bound;
                }
            }
            catch (LdapException ex)
            {
                return false;
            }
        }

        /// <summary>
        /// User full id 
        /// </summary>
        /// <param name="userId">User name</param>
        /// <returns>userName@domain</returns>
        public string UserFullId(string userId)
        {
            string value = string.Format(@"{0}@{1}", userId, DomainName);
            return value;
        }
    }
}

Here, we are using the LDAP manager class to validate username and password:

string domain = "LdapdomainNameOrIp.com";
int port = 389;
string user = "user.name";
string password = "password@123";
bool isValied = new LdapManager(domain, port).Validate(user, password);

Source Code

It is a Visual Studio 2017 solution with console projects:

• DotNet: .NET Framework 4.6.1
• DotNetCore: .NET Core 2.2

References

• Validate a username and password against Active Directory?
• Application Login through Active Directory (LDAP)
• ASP.NET Core 2.0 LDAP Active Directory Authentication
• Working with DirectoryServices in ASP.NET Core

Limitations

• The LDAP path may not be simple as mine so fix it as needed.
• The code may throw an error for untested inputs, if may please let me know

History

• 15^th July, 2020: Initial version