If you set a MediaWiki install with VisualEditor installed to be private, it will die on the spot.
What I mean is that if you set the wiki to require a logon to even view the content (a completely private wiki) and you have VisualEditor installed, then all pages will return a 500 Server Error.
The fix that we found that works most easily is the “Forwarding Cookies to Parsoid” solution here:
which means in reality to just one line to LocalSettings.php. The comment are also helpful, to clarify the issues involved:
// Forward users' Cookie: headers to Parsoid. Required for private wikis (login required to read).
// If the wiki is not private (i.e. $wgGroupPermissions['*']['read'] is true) this configuration
// variable will be ignored.
// WARNING: ONLY enable this on private wikis and ONLY IF you understand the SECURITY IMPLICATIONS
// of sending Cookie headers to Parsoid over HTTP. For security reasons, it is strongly recommended
// that $wgVirtualRestConfig['modules']['parsoid']['url'] be pointed to localhost if this setting is enabled.
$wgVirtualRestConfig['modules']['parsoid']['forwardCookies'] = true;
If the security implications are acceptable, then this works perfectly.