Since we didn't find solution for auto create user on login , while using LDAP authentication, I wrote a small feature to do that

The feature is auto create user on login
User will be created only if the user exists in LDAP.
The algorithm is like that:

If user already Exist in Jira continue as usual, nothing changed
If user don't exist in Jira create the user (add him to jira-users and jira-developers and autocreated-users group and also set his mail (hard coded : username@amdocs.com), autocreated-users group will be created if not exist )
on LDAP authentication: check if user exist in LDAP
if user not exist in LDAP delete it
authenticate the user in LDAP
user logged in

In order to implement this feature (by the way it was tested on Jira 3.6 only), I attached zip file with sources and classes
extract the com.zip file and put the sub directories under : [jira installation]\WEB-INF\classes\com

We find it very useful, hope it will be included in Jira future versions
Meir Ivgi