In OIM, while user creation, the Auto Group Membership Event handler is used to evaluate the membership rules and based upon these membership rules, the roles are automatically assigned to the newly created user. After the roles are assigned to the user, the evaluate user policies scheduled job runs to automatically provision resources based upon the user role.
I recently faced an issue in which the auto group membership event handler was not firing during user creation, so i raised a case with Oracle Support and found out that apparently, the custom event handlers written by me for populating certain fields such as user login were interfering with the built in event handler. To resolve this issue, i increased the order of firing of my event handlers to very high values specifically 20,000,20001 and this increase in value ensured that my event handlers did not interfere with the built in event handler and this resolved the problem.
You can change the order of event handlers by using mds explorer to modify the customeventhandler.xml file.
<action-handler class="com.blogspot.ramannanda.oim.handlers.GenerateEmailId" entity-type="User" operation="CREATE" name="GenerateEmailId" stage="postprocess" order="200000" sync="FALSE"/>
Hope this helps.
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