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Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 12.0.2): 14.0.4.2
Operating system and version (eg, Ubuntu 17.04): Fedora 28
Apache or nginx version (eg, Apache 2.4.25): nginx 1.12.1-8
PHP version (eg, 7.1): 7.2.12-1
The issue you are facing:
After upgrading Fedora from 27 to 28 I can no longer login. I am always returned to the login form with the url: /login?redirect_url=/apps/files/
Is this the first time you’ve seen this error? (Y/N): N
The unexplained redirect back to login I’ve seen during the setup stage several months ago. I ended up removing all the install files and re-installing nextcloud to get it working.
Steps to replicate it:
- Installed Nextcloud 14.0.3 on Fedora 27 from source package.
- Upgraded Fedora 27 to 28
- Tried to login
The output of your Nextcloud log in Admin > Logging: https://paste.fedoraproject.org/paste/KVC4Lye4p9lQTfCYwLzbGg
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!): https://paste.fedoraproject.org/paste/ZTyIQa7Qh0wnzqxi~oCoRA
The output of your Apache/nginx/system log in /var/log/____: Nothing is logged when I try to login or just load the login page.
What I’ve tried so far;
- Upgrade nextcloud from 14.0.3 to 14.0.4.2 using the updater.phar.
- Turn maintenance mode on/off
- Set loglevel to 0 in nextcloud config.php
- run occ maintenance:repair
- Move my datadirectory from the old NFS share that was working to a CIFS share which is mounted using the nginx user/group. Same user/group as php-fpm and nginx are using.
- Nothing is logged to the browser developer console when I login. I get a 303 status from the POST request.
- Set selinux to permissive.
- Checked oc_bruteforce_attempts, it was empty.
- Disabled auth.bruteforce.protection.enabled in config.php
- Checked php-fpm log, nothing is logged during failed login attempt.
- Tried logging in both as admin and as another user. Same issue.
- Cleared all cookies and data for nextcloud in my browser.
Noteworthy is that Fedora 28 switched from php 7.1 to php 7.2. I’m not allowed to install 3rd party repos to downgrade back to 7.1.