Currently, it is not possible to create issues in JSD enabled projects through the IssueManager because it does not take account of the new Service Desk Customer - Portal Access security type, the same is true for all other security checks like comment, add attachments etc. The createIssueObject method below fails with a CreateException, indicating (for create) that the user does not have the CREATE_ISSUE permission:

ComponentAccessor.getIssueManager().createIssueObject(anIssueObject.getReporterUser(), anIssueObject);

The workaround I have applied is to modify the Projects Permission Scheme to add the Role Service Desk Customers for each related JIRA Permission thats required, and this works. The user involved does not start counting toward the JIRA user count (primary attribute of a JSD Portal User), and issues can be created and updated. But, there is then a scary error warning on the Service Desk admin screen:

Two things:
1. API issue creation with portal users as the issue reporter should just work, it doesn't.
2. I'm not sure what ill effects there would be over the workaround of adding Service Desk Customers role in the permission scheme, comments regarding scary warning above?