With the ocdav service being able to provided signed download URLs we
need the proxy to be able to verify the signatures.
This should also be a first step towards phasing out the weird ocs based
client side signed urls.
Related Tickets: #1104
The old approach of the authentication middlewares had the problem that when an authenticator could not authenticate a request it would still send it to the next handler, in case that the next one can authenticate it. But if no authenticator could successfully authenticate the request, it would still be handled, which leads to unauthorized access.
