I have restricted a project to a specific group. but want to show a ticket to anyone who is been tag

[syed sadiq]

I have a secure project for internal dept which they want accessible to their team only.

But there is a catch that if someone from that team tag (@mention) someone outside of the team, the issue should be only visible to that person as well.

[Brant Schroeder · Accepted solution]

If the individual does not have access to the issue your team will not be able to @mention them.  I would suggest creating a custom field called collaborators making it a multiple user picker.  Then on the projects permission scheme you can give that custom field browse projects.  This will then allow anyone added to the custom field to see the issue.  If I remember correctly it will only give them access to see the issues that they are on.  I believe that it might also give everyone access to know the project exists but they can not see any issues in the project.  

[syed sadiq]

Thank you so much! I have tried it and so far its working as ecpected.