Is it possible to have permission levels for each workflow transition

[Kate]

If I'm creating a project where the different transitions would need to be controlled by different project specific roles (not groups), how do I go about it? 

In essence, I'm wondering if it's possible at the Role level or better yet at the permission schema level to only allow "people in the validators Role" to press the "Assign" button or only "people in the developer role" to press the "in progress" button etc.)

[Nic Brough {Adaptavist}]

It's even more flexible than that.  Have a look at the "conditions" on the workflow transitions and you'll see two broad types - direct and indirect.  Direct ones say things like "only people in role X can do this".  Indirect ones say things like "only people with permission Y can do this" - they go through the permission schemes.

In fact, you're generally discouraged from using groups in conditions at all, roles are the better way to do it.  Have a look at the built in workflows to see how they do it.

[Sten Sundelin]

You do that in the workflow, on each transition you'll create/set a condition to only allow users in specific groups/roles to perform the transition. If they're not permitted, they won't see the button or dropdown option.