OK, let me try to explain. I hope I can put it in simple terms. You say Nextcloud is installed under "
www.mydomain.fr". But your Roundcube installation is on a different server. I therefore assume that you will reach your Roundcube for example under "roundcube.yourserver. fr". This is a crossdomain setup because both URLs come from different servers.
If Roundcube were under "roundcube.mydomain.fr", this would still be crossdomain. If Nextcloud is under "
www.mydomain.fr:443" and Roundcube under "
www.mydomain.fr:80" this is also crossdomain.
If it were "
www.mydomain.fr/nextcloud/" for NextCloud and "
www.mydomain.fr/roundcube/" for Roundcube, this would NOT be a cross domain setup.
Crossdomain setups have a security problem. At least in relation to Javascript. Therefore, these should be avoided as far as possible. There are also ways to implement cross domain setups with Javascripts, but the HTTP headers of the server, in this case of the next cloud server, have to be adapted. The Nextcloud server should be configured to send the following headers correctly:
Access-Control-Allow-Origin: *
Access Control Allow Allow Methods: GET, POST, OPTIONS, PROPFIND, PROPPATCH, REPORT, PUT, MOVE, DELETE, LOCK, UNLOCK
Access Control Allow Headers: User-Agent, Authorization, Content-type, Depth, If-match, If-None-Match, Lock-Token, Timeout, Destination, Overwrite, Prefer, X-client, X-Requested-With
Access-Control-Expose-Headers: Etag, Preference-Applied
For information on how to set these headers, see the server documentation. For a little bit more detailed information, you can have a look at
https://www.inf-it.com/caldavzap/readme.txtConcerning the globalSubscribedCalendars: For the reasons mentioned above, these also only work if the CalDAV server sends the correct CORS headers. Google, for example, does not send them. Thus a subscription of Google calendars is only possible via workarounds. Keyword: nginx proxying