Yo lo tengo hecho asi. A ver si te sirve
Código PHP:
<connectionStrings>
<add name="ADConnectionString" connectionString="LDAP://nombreservidorAD.extension/CN=catalogo,DC=nombreservidorAD,DC=extension"/>
</connectionStrings>
<system.web>
<compilation debug="true" strict="false" explicit="true">
<assemblies>
<add assembly="System.DirectoryServices, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
</assemblies>
</compilation>
<authentication mode="Forms">
<forms name=".ADAuthCookie" timeout="1"/>
</authentication>
<authorization>
<deny users="?"/>
<allow users="*"/>
</authorization>
<membership defaultProvider="MyADMembershipProvider">
<providers>
<add
name="MyADMembershipProvider"
type="System.Web.Security.ActiveDirectoryMembershipProvider, System.Web, Version=2.0.0.0,
Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
attributeMapUsername="sAMAccountName"
connectionStringName="ADConnectionString"
connectionUsername="nombreservidorAD\usuario"
connectionPassword="password"/>
</providers>
</membership>
</system.web>
Saludos