Let’s face it, you found this blog post because like me you found Jira permissions to be ten times more confusing than necessary. After a really really long time, I figured out how to give a user access to just one project instead of every project on my account.
1. Copy the default permission scheme to another like “Project-Client-Permissions”
2. Create a group, “Project-Client”
3. Add that group only to the permissions you want them to have. For me, it is Browse Project, Create Issues, Edit Issues, Resolve Issues, Add Comments, Edit Own Comments, Delete Own Comments, Create Attachments, and Delete Own Attachments
4. Apply that Permission scheme to the project
5. Add a user and add them only to the Project-Client group (they should also be in jira-users by default so they can login)
6. One additional step I did – edit the permissions of the default permission scheme and remove “Application Access” – “Any logged in user” from the “browse projects” permission in order to hide other projects from my one project user.