Add the native keyring to the documentation (#15596)

docs/concepts/authentication/http.md

@@ -5,14 +5,8 @@ uv supports credentials over HTTP when querying package registries.
 Authentication can come from the following sources, in order of precedence:
 
 - The URL, e.g., `https://<user>:<password>@<hostname>/...`
-- A [`.netrc`](https://everything.curl.dev/usingcurl/netrc) configuration file
+- A [netrc](#netrc-files) configuration file
-- A [keyring](https://github.com/jaraco/keyring) provider (requires opt-in)
+- A [keyring provider](#keyring-providers) (off by default)
-
-`.netrc` authentication is enabled by default, and will respect the `NETRC` environment variable if
-defined, falling back to `~/.netrc` if not.
-
-To enable keyring-based authentication, pass the `--keyring-provider subprocess` command-line
-argument to uv, or set `UV_KEYRING_PROVIDER=subprocess`.
 
 Authentication may be used for hosts specified in the following contexts:
 
@@ -22,6 +16,47 @@ Authentication may be used for hosts specified in the following contexts:
 - `find-links`
 - `package @ https://...`
 
+## netrc files
+
+[`.netrc`](https://everything.curl.dev/usingcurl/netrc) files are a long-standing plain text format
+for storing credentials on a system.
+
+Reading credentials from `.netrc` files is always enabled. The target file path will be loaded from
+the `NETRC` environment variable if defined, falling back to `~/.netrc` if not.
+
+## Keyring providers
+
+A keyring provider typically fetches credentials from an operating system store.
+
+The keyring providers are not used by default.
+
+### The 'subprocess' keyring provider
+
+The 'subprocess' keyring provider invokes the `keyring` command to fetch credentials.
+
+The expected interface for this is based on the popular [keyring](https://github.com/jaraco/keyring)
+Python package. Similar support is built-in to pip.
+
+Set `--keyring-provider subprocess`, `UV_KEYRING_PROVIDER=subprocess`, or
+`tool.uv.keyring-provider = "subprocess"` to use the provider.
+
+### The 'native' keyring provider
+
+!!! note
+
+    The native keyring provider is in [preview](../preview.md) — it is still experimental and being
+    actively developed.
+
+The native keyring provider uses the secret storage mechanism native to your operating system. On
+macOS, it uses the Keychain Services. On Windows, it uses the Windows Credential Manager. On Linux,
+it uses the DBus-based Secret Service API.
+
+Currently, uv only searches the native keyring provider for credentials it has added to the secret
+store.
+
+Set `--keyring-provider native`, `UV_KEYRING_PROVIDER=native`, or
+`tool.uv.keyring-provider = "native"` to use the provider.
+
 ## Persistence of credentials
 
 If authentication is found for a single index URL or net location (scheme, host, and port), it will