I used this at some point in the past, not sure if it helps

Procedure verifyIfUserExists(tcUserId)
		Local lcUserId
		lcUserId ='CN='+tcUserId
		objRootLDAP = Getobject("LDAP://RootDSE")
		strDNSDomain = objRootLDAP.Get("DefaultNamingContext") && Get the context
		strGroup = "CN=oeb-test,"
		strOU = "OU=Test,OU=OEB,OU=SAAS-users,"
		*' Prepare the OU and the Group
		objGroup = Getobject("LDAP://"+ strGroup + strOU + strDNSDomain)
		objOU =Getobject("LDAP://" +strOU + strDNSDomain)

		For Each objUser In objOU && Add the user to the correct group
			If objUser.Class = Lower("User")
				If objUser.Name = lcUserId
					Return .T.
				Endif
			Endif
		Endfor
		Return .F.

	Endproc

>>>>Hi,
>>>>
>>>>In my ASP.NET application, MS .NET Framework has a class that allows to get a user name and email by AD username.
>>>>
>>>>Could the same be done in VFP 9?
>>>>
>>>>That is, user would enter his/her AD username (e.g. "j_smith") and the VFP application would connect to the AD (using the entered username) and get this user name and email?
>>>>
>>>>Let me know if you have done something like this
>>>>
>>>>TIA
>>>
>>>The approach suggested by Tamar is nice. But the customer won't want my VFP application to SQL Select all records from the AD. Instead they want the application to "know" - or determine - the AD username currently logged into the PC.
>>>
>>>That is, suppose when a user logs into his/her PC, they enter the AD username "j_smith" (as an open text) and enter the password (of course, covered with asterisks). Then, they want my VFP application to determine (how is a big question) that the current AD username (logged into the PC) is j_smith.
>>>
>>>Is the above possible?
>>
>>When a user signs in to on-premises AD, several environment variables are set:
>>USERDNSDOMAIN
>>USERDOMAIN
>>USERNAME
>>
>>You could retrieve these with GETENV(). Bear in mind these can be modified by the user so they're not reliable in an adversarial situation.
>>There are also the old ID( ) and SYS( 0 ) functions. I'm not sure if these return the correct username if the user modifies the environment variables.
>>
>>I haven't tested any of the above for a user sign in to Azure Active Directory (AAD), if that applies in your case. I suspect not, since those usernames are of the format someuser@somedomain.com .
>
>Thank you for your message.
>Now - just this morning (since the customer is in Europe) - I received a new requirement. Now the customer wants a user to enter both the AD username and AD password into my VFP application. And my VFP application to check if this is a valid user. Initially I thought that they would not want a user to enter his/her password into the VFP application.
>So, I am back to Tamar's link where the VFP application should create a query to the AD and validate a user.
>I will need to find the name of the AD/SQL Server DB to do that.