<add name="ADConnectionString" connectionString="LDAP://FullyQualifiedServerName:636/OU=XXX,DC=XXX,DC=XXX" />
<add name="ADMembershipProvider"
type="System.Web.Security.ActiveDirectoryMembershipProvider, System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
 connectionStringName="ADConnectionString"
 connectionUsername="CN=XXX,OU=XXX,DC=XXX,DC=XXX" connectionPassword="XXXXXX"
 connectionProtection="Secure" enableSearchMethods="true" enablePasswordReset="true"
 requiresQuestionAndAnswer="true" applicationName="XXXX"
 description="Default AD connection" requiresUniqueEmail="false"
 clientSearchTimeout="30" serverSearchTimeout="30" attributeMapPasswordQuestion="xxx"
 attributeMapPasswordAnswer="xxxx" attributeMapFailedPasswordAnswerCount="xxxx"
 attributeMapFailedPasswordAnswerTime="xxxx"
 attributeMapFailedPasswordAnswerLockoutTime="xxxx" attributeMapEmail="mail"
 attributeMapUsername="userPrincipalName" maxInvalidPasswordAttempts="7"
 passwordAttemptWindow="1" passwordAnswerAttemptLockoutDuration="5"
 minRequiredPasswordLength="8" minRequiredNonalphanumericCharacters="0"
 passwordStrengthRegularExpression="^(?=.*d)(?=.*[a-z])(?=.*[A-Z])(?!.*s).{8,20}$" />

return Membership.Providers["ADMembershipProvider"].ValidateUser(userName, userPassword);