How to associate a worker with user ID using X++ and add External Relation

Hi all,

I need assistance to associate an AX user with a person  (Vendor Contact that I have already created) using x++  and then assign an External Vendor relation so the Vendor contact person can access AX through  enterprise portal.  Data sources on user relations form (System admin-> User relations -> new) shows: DirpersonUser.PersonParty,  UserExternalParty,  and UserInfo.  I  wonder if anyone can assist?

Thanks.