chore(docs): add highlight post for secrets in disk buffers (#18994)

* chore(docs): add highlight post for secrets in disk buffers

* Apply suggestions from code review

Co-authored-by: May Lee <mayl@alumni.cmu.edu>

---------

Co-authored-by: Jesse Szwedko <jesse.szwedko@datadoghq.com>
Co-authored-by: May Lee <mayl@alumni.cmu.edu>

website/content/en/highlights/2023-10-30-secrets-in-disk-buffers.md

@@ -0,0 +1,83 @@
+---
+date: "2023-10-30"
+title: "Secrets in Disk Buffers"
+description: ""
+authors: ["tobz"]
+pr_numbers: [18816]
+release: "0.34.0"
+hide_on_release_notes: false
+badges:
+  type: "announcement"
+---
+
+Starting with Vector's `0.34.0` release, secrets in events will now be stored in disk buffers. These
+secrets are stored **unencrypted**.
+
+## Event secrets
+
+For some source components in Vector, such as the Datadog Agent or Splunk HEC sources, these
+components have the ability to store the API key received in requests by Vector in order to re-use
+the same API key when sending those events back out to a compatible service. This allows users, for
+example, to set up Vector as an aggregator for all of their Datadog Agent processes, reusing the
+original API key, or keys, as the events are then forwarded to the Datadog API.
+
+## Disk buffers and event secrets and metadata
+
+Prior to [#18816](https://github.com/vectordotdev/vector/pull/18816), these event secrets (and other
+event metadata) were not stored when using disk buffers. This represented a loss of functionality
+when users switched from the default in-memory buffers to disk buffers. In order to bring this
+functionality up to par, we added support for storing event secrets/metadata when writing events to
+disk buffers.
+
+Naturally, event secrets represent sensitive data such as API keys and more. However, Vector
+currently stores these event secrets **unencrypted** in disk buffers.
+
+## Do I need to worry about this change?
+
+Firstly, if you're **not** using disk buffers, then there is no change to Vector's behavior and you can
+stop reading here.
+
+There are two main scenarios where a configuration might now start storing secrets in disk buffers:
+
+- When you are using a source component which has the ability to store secrets
+- When you are using `remap` and adding secrets directly to events
+
+### Source components that can store secrets
+
+Some source components store secrets (specifically, API keys) on an event in order to
+facilitate Vector acting similarly to a proxy, using as much of the original request/event data as
+possible. Only two sources currently provide such behavior:
+
+- `datadog_agent` source (stores the `DD-API-KEY` header value; **enabled** by default)
+- `splunk_hec` source (stores the `Authorization` header value; **disabled** by default)
+
+However, for both of these sinks, this behavior can be disabled by setting `store_api_key` to
+`false` for the `datadog_agent` source, or setting `store_hec_token` to `false` for the `splunk_hec`
+source.
+
+### Manually-stored secrets using `remap`
+
+When using the `remap` transform, VRL exposes helper functions to set secrets on events. If your
+`remap` usage includes setting secrets, then those secrets would also now be in scope for getting
+stored in disk buffers.
+
+## Securing disk buffers
+
+As mentioned above, secrets will now be stored in disk buffer data files, and will be
+**unencrypted**. The data directory that Vector is configured to use should be locked down as
+tightly as possible so that only the user/group that runs the Vector process has read/write
+access.
+
+By default on Unix-based platforms, Vector will attempt to set file permissions for the disk buffer
+directory/files to only be readable/writeable by the process user, and only readable by the process
+group. This does not occur on Windows.
+
+## Future improvements to disk buffers and securely buffering events
+
+This is not the end of the story for storing secrets in disk buffers. We do have tentative plans to
+eventually support encrypting secrets in disk buffers, and potentially support encrypting all event
+data itself. This work depends on capabilities Vector does not currently have, such as being able to
+securely pass a decryption key into the process, and where a long-lived decryption key would live.
+
+These issues need to be tackled first before we can provide a robust encryption solution for disk
+buffers.