Provide a REST API endpoint to retrieve permissions of users (including browse project permissions for JSM customers)

Problem Definition

We don't have an end point to use for JSM projects to check the permissions of users. Using the Jira REST API endpoint /rest/api/3/mypermissions doesn't explain how some users have access to projects (in case of Portal access as customers) and it actually returns results that are contradicting the ones you get by calling: 

• POST /rest/api/3/permissions/project
• POST /rest/api/3/permissions/check

Steps to reproduce

1. Create a JSM project and make sure that Browse Project permissions have been granted to Service Project Customer - Portal Access and that Customer permissions - Service Project access configuration is set to Anyone on the web
2. As Jira user that has no access to this project, send a GET request to "/rest/api/3/mypermissions?permissions=BROWSE_PROJECTS&projectId=<projectId>" where  <projectId> is the ID of the project created in previous step. See that the user has browse project permission.
3. Now, as the same user, send a REST API request to the POST /rest/api/3/permissions/project endpoint

Expected Results

The outcome is consistent with the one of the previous REST API call and the project created in step #1 is returned

Actual Results

The project created in step #1 is not returned.
 

Suggested Solution

Add a JSM REST API endpoint that would retrieve and point out portal access browse permissions if any.

Workaround

None