Previously, when a user initiated a websocket subscription,
the access to the `sys/events/subscribe` endpoint was checked then,
and only once.
Now, perform continuous policy checks:
* We check access to the `sys/events/subscribe` endpoint every five
minutes. If this check fails, then the websocket is terminated.
* Upon receiving any message, we verify that the `subscribe`
capability is present for that namespace, data path, and event type.
If it is not, then the message is not delivered. If the message is
allowed, we cache that result for five minutes.
Tests for this are in a separate enterprise PR.
Documentation will be updated in another PR.
Co-authored-by: Tom Proctor <tomhjp@users.noreply.github.com>
Co-authored-by: Nick Cabatoff <ncabatoff@hashicorp.com>
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