In a previous post I walked through the configuration needed to setup the workflow for the user request. You can see that post here.
In this video I go through the user request process as a HR manager and IT manager might work the process.
Now every company is different in their internal procedures, and their size will also determine how much automation is needed here. This process might also started from IT and users get added to the system based on the active directory security groups they belong to. Other companies might not use the HR module in Dynamics AX and use an external solution, in which case using AD groups and the automatic role assignment might be handy features over using this work flow to request access.