OwnCloud uses Wikipedia:cURL and Wikipedia:SabreDAV to check if WebDAV is enabled. If you use a SSL/TLS with a self-signed certificate, e.g. as shown in LAMP and access ownClouds admin panel, you will see the following error message:

Your web server is not yet properly setup to allow files synchronization because the WebDAV interface seems to be broken.

In order to circumvent this problem a few solutions are available. One is to turn off the VERYFIPEER-parameter in cURL which is strongly discouraged as it will effectively render any encryption useless (see: https://github.com/owncloud/core/issues/1909#issuecomment-14107259).

A better way is to trust your own certificate. Assuming that you followed the LAMP-tutorial, execute the following steps:

Create local directory for non-distribution certificates and copy LAMPs certificate there. This will prevent ca-certificates-updates to overwrite it.

$ mkdir -p /usr/share/ca-certificates
$ cp /etc/httpd/conf/server.crt /usr/local/share/ca-certificates/nas.lan.crt

Add nas.lan.crt to /etc/ca-certificates.conf:

nas.lan.crt

Now, regenerate your certificate store:

$ update-ca-certificates

Restart the httpd service to activate your certificate.