Users cannot transition issues via the customer portal without the Assign Issues permission

Issue Summary

If a user (licensed or portal only customer) does not have the Assign Issues permission they are unable to transition any issues via the customer portal.

Steps to Reproduce

1. Create a JSD project.
2. Create a customer-facing transition in your workflow that appears on the customer portal.
3. Create a ticket in the project and assign this to a user.
4. Remove the permissions for your user from the Assign Issues permission in the project's permission scheme.
5. Transition the issue via the Jira issue view.
6. Transition the issue via the customer portal

Expected Results

The issue should be transitioned via both the Jira issue view or the customer portal.

Actual Results

The issue can only be transitioned via the Jira issue view, transitioning via the customer portal results in the below error:
The below exception is thrown in the xxxxxxx.log file:

{
  "errors": [
    {
      "errorMessage": "You do not have permission to assign issues."
    }
  ],
  "reasonKey": "transition failed validation",
  "reasonCode": "400"
}

Workaround

Grant the assign user permission to any users who may need to make transitions via the customer portal.
Especially Service Desk Customer - Portal Access as this will allow your portal only customers to execute the transition you have made available to them.