Thanks. I guess I am close now. 
I am getting this now - which probably means I should specify my LDAP “secret” somewhere in Tyk/TIB.
ERRO[0779] [AD AUTH] Bind failed for user:
ERRO[0779] [AD AUTH] --> Error was: LDAP Result Code 53 “Unwilling To Perform”: unauthenticated bind (DN with no password) disallowed
Any pointer to where do I specify it, or is it something else?