feat(metrics): basic auth support (#1579)

* feat(internal): add basic auth HTTP middleware

Signed-off-by: Xe Iaso <me@xeiaso.net>

* feat(config): add HTTP basic auth for metrics

Signed-off-by: Xe Iaso <me@xeiaso.net>

* feat(metrics): wire up basic auth

Signed-off-by: Xe Iaso <me@xeiaso.net>

* doc: document HTTP basic auth for metrics server

Signed-off-by: Xe Iaso <me@xeiaso.net>

* chore: spelling

Signed-off-by: Xe Iaso <me@xeiaso.net>

* docs(admin/policies): give people a python command

Signed-off-by: Xe Iaso <me@xeiaso.net>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>

docs/docs/CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add Bulgarian locale ([#1394](https://github.com/TecharoHQ/anubis/pull/1394))
 - Fix CEL internal errors when iterating `headers`/`query` map wrappers by implementing map iterators for `HTTPHeaders` and `URLValues` ([#1465](https://github.com/TecharoHQ/anubis/pull/1465)).
 - Enable [metrics serving via TLS](./admin/policies.mdx#tls), including [mutual TLS (mTLS)](./admin/policies.mdx#mtls).
+- Enable [HTTP basic auth](./admin/policies.mdx#http-basic-authentication) for the metrics server.
 
 ## v1.25.0: Necron
 

docs/docs/admin/policies.mdx

@@ -171,6 +171,24 @@ metrics:
 
 As it is not expected for certificate authority certificates to change often, the CA certificate will NOT be automatically reloaded when the respective file changes.
 
+### HTTP basic authentication
+
+Anubis' metrics server also supports setting HTTP basic auth as a lightweight protection against unauthorized users viewing metrics data. As the basic auth credentials are hardcoded in the configuration file, administrators SHOULD use randomly generated credentials, such as type-4 UUIDs or other high entropy strings. These credentials MUST NOT be sensitive or used to protect other high value systems.
+
+Configure it with the `basicAuth` block under `metrics`:
+
+```yaml
+metrics:
+  bind: ":9090"
+  network: "tcp"
+
+  basicAuth:
+    username: azurediamond
+    password: hunter2
+```
+
+If you have Python installed, you can generate a high entropy password with `python -c 'import secrets; print(secrets.token_urlsafe(32))'`.
+
 ## Imprint / Impressum support
 
 Anubis has support for showing imprint / impressum information. This is defined in the `impressum` block of your configuration. See [Imprint / Impressum configuration](./configuration/impressum.mdx) for more information.