Hello, I am trying to solve what seems like a common problem. I think I understand what the problem is but I cannot find out where to edit to solve it. PDFs do not display in viewer, showing only a blank page. This depends on an incorrect conflicting X-Frame-Options value but I cannot understand in which configuration file this value is. My search for the error has shown a very probable cause and explanations of the value to edit, but not where the file to be edited is located.
Steps to reproduce
1. Open any PDF (not corrupt, normally readable)
PDF is displayed in PDF viewer page
Blank page is shown
Operating system: Ubuntu 16.04
Web server: Apache2
PHP version: 7.0.15
ownCloud version (see ownCloud admin page): 9.1.4
Updated from an older ownCloud or fresh install: fresh
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption):
"Refused to display [PDF] in a frame because it set multiple 'X-Frame-Options' headers with conflicting values ('DENY, SAMEORIGIN, SAMEORIGIN'). Falling back to 'deny'."
It appears I should edit the value to SAMEORIGIN only. The error appears to depend on NGINX reverse proxy and a related post is displayed, but I cannot understand how to edit as I have no /etc/nginx directory in my directory tree and I do not know how this works.
Thank you for any assistance.