This aligns the recommended setting with the max-age of `15768000` as described in our documentation. Furthermore it fixes some logical problems with the code, unit tests has been added as well.
Fixes https://github.com/owncloud/core/issues/16673
Without /dev/urandom being available to read the medium RNG will rely only on the following components on a Linux system:
1. MicroTime: microtime() . memory_get_usage() as seed and then a garbage collected microtime for loop
2. MTRand: chr((mt_rand() ^ mt_rand()) % 256)
3. Rand: chr((rand() ^ rand()) % 256)
4. UniqId: Plain uniqid()
An adversary with the possibility to predict the seed used by the PHP process may thus be able to predict future tokens which is an unwanted behaviour.
One should note that this behaviour is documented in our documentation to ensure that users get aware of this even without reading our documentation this will add a post setup check to the administrative interface.
Thanks to David Black from d1b.org for bringing this again to our attention.
Doing this in the PHP code is not the right approach for multiple reasons:
1. A bug in the PHP code prevents them from being added to the response.
2. They are only added when something is served via PHP and not in other cases (that makes for example the newest IE UXSS which is not yet patched by Microsoft exploitable on ownCloud)
3. Some headers such as the Strict-Transport-Security might require custom modifications by administrators. This was not possible before and lead to buggy situations.
This pull request moves those headers out of the PHP code and adds a security check to the admin settings performed via JS.
