Programmatically obtain a list of Active Directory groups that an individual is a member of

Here is some sample code that will allow you to obtain a complete list of all of the Active Director groups that a specified user is a member of:

public void GetGroupsUserIsMemberOf(string sAMAccountName)
{
    try
    {
        using (DirectoryEntry dirEntry = new DirectoryEntry())
        {
            dirEntry.Path = "LDAP://OU=OUName,DC=DCName,DC=org";
            dirEntry.AuthenticationType = AuthenticationTypes.Secure;

            using (DirectorySearcher dirSearch = new DirectorySearcher(dirEntry))
            {
                dirSearch.Filter = string.Format("(&(objectCategory=person)(objectClass=user)(SAMAccountName={0}))", sAMAccountName);
                dirSearch.PropertiesToLoad.Add("memberOf");
                SearchResult result = dirSearch.FindOne();
                if (result != null)
                {
                    int propCount = result.Properties["memberOf"].Count;
                    for (int i = 0; i <= propCount - 1; i++)
                    {
                        // Clean up the name of the group for display purposes
                        char[] delim = new char[] { ',', '\\' };
                        string groupName = result.Properties["memberOf"][i].ToString().Split(delim).First().Replace("CN=", string.Empty);
                        Console.WriteLine(string.Format("Group# {0}: {1}", i+1, groupName);
                    }
                }
            }
        }
    }
}

Programmatically obtain user information from Active Directory

Here is a sample method that you can use for contacting Active Directory in order to obtain information about a user based on his/her username/account name (a.k.a. sAMAccountName in AD):

public void GetUserDistinguishedName(string sAMAccountName)
{
    using (DirectoryEntry dirEntry = new DirectoryEntry())
    {
        dirEntry.Path = "LDAP://OU=OUName,DC=DCName,DC=org";
        dirEntry.AuthenticationType = AuthenticationTypes.Secure;

        using (DirectorySearcher dirSearch = new DirectorySearcher(dirEntry))
        {
            dirSearch.Filter = string.Format("(&(objectCategory=person)(objectClass=user)(SAMAccountName={0}))", sAMAccountName);
            SearchResult result = dirSearch.FindOne();
            if (result != null)
            {
                Console.WriteLine(string.Format("Distinguished Name: {0}" ,result.Properties["distinguishedname"][0].ToString()));
                Console.WriteLine(string.Format("First Name: {0}", result.Properties["givenname"][0].ToString()));
                Console.WriteLine(string.Format("Last Name: {0}", result.Properties["sn"][0].ToString()));
                Console.WriteLine(string.Format("Email Address: {0}", result.Properties["mail"][0].ToString()));
            }
        }
    }
}

Programmatically obtain a list of all properties associated with a user's profile in Active Directory

The following simplified code sample can be used for obtaining a list of all possible properties that are associated with a user's profile in Active Directory.  This code would be useful if you're trying to figure out which AD properties you may need to access to get the information you require:

using System.DirectoryServices;

...

try
{
   using (DirectoryEntry dirEntry = new DirectoryEntry("LDAP://yourOUPath))
   {
      using (DirectorySearcher dirSearch = new DirectorySearcher(dirEntry))
      {
         dirSearch.Filter = "(&(objectClass=user)(sAMaccountname=yourADLoginName))";
         SearchResult result = dirSearch.FindOne();
         if (result != null)
         {
            foreach (string propertyName in result.Properties.PropertyNames)
            {
               Console.WriteLine(propertyName);
            }
         }
      }
   }
}
catch (Exception ex)
{
   Console.WriteLine(ex.Message);
}

Likely culprits for issues with this code could be attributed to the following items:

1. There could be issues with the structure of the LDAP path
2. You may need to specify a DirectoryEntry.Username and DirectoryEntry.Password
3. You may need to define a DirectoryEntry.AuthenticationType