Navigating to private issues in a public repo doesn't trigger authentication

Summary

When a user visits the /issues page of a public available project, and if the project has issues set at private scope (i.e. visible only to project members) through project setting - permissions, navigation attempt to the project's issues page would render a 404 response.

Steps to reproduce

1. create a public repo and set the issues visibility to "project members"
2. logout from gitlab
3. navigate to the project's /issues link
4. page says 404

Example Project

https://gitlab.com/yuanchenlu/hello/issues

What is the current bug behavior?

404 response at the above link

What is the expected correct behavior?

authentication flow to log in

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

N/A

Results of GitLab application Check

N/A

Possible fixes

https://gitlab.com/yuanchenlu/gitlab-ce/commit/ea2a593545b6d9dcbfc98f6bbc09b2cfde11edf2