In JIRA version 4.2.4 there is an "Assign To Me" button in the issue details screen which allows the user to change the issue's assignee value without going through one of the user defined workflow steps. This defeats the purpose of having configurable workflows steps since the user is able to change the state of the issue outside of the workflow. There should be a way to configure JIRA so that this button can be hidden or disabled.

An admin should also have the ability to hide the Assign menu button on the top of a ticket for the same purposes as listed above. If a user wants to only have the assignee determined by a workflow, this hinders that ability.

Workaround:
For JIRA Server: Go to Admin, Plugins, System Plugins, Issue Operations Plugin, Manage plugin modules. Find the module named "View Issue Ops Bar Assign To Me Link (assign-to-me)" and click on the Disable button. The "Assign To Me" button will now not be displayed when viewing any issue.

 This is not available on JIRA Cloud because System Plugins are restricted.

Another workaround using CSS:

• How to hide the "Assign" and "Assign to me" links via CSS