bake: remote auth variables

Signed-off-by: David Karlsson <35727626+dvdksn@users.noreply.github.com>

content/build/bake/remote-definition.md

@@ -179,3 +179,19 @@ docker buildx bake -f bake.hcl -f cwd://local.hcl "https://github.com/crazy-max/
   }
 }
 ```
+
+## Remote definition in a private repository
+
+If you want to use a remote definition that lives in a private repository,
+you may need to specify credentials for Bake to use when fetching the definition.
+
+If you can authenticate to the private repository using the default `SSH_AUTH_SOCK`,
+then you don't need to specify any additional authentication parameters for Bake.
+Bake automatically uses your default agent socket.
+
+For authentication using an HTTP token, or custom SSH agents,
+use the following environment variables to configure Bake's authentication strategy:
+
+- [`BUILDX_BAKE_GIT_AUTH_TOKEN`](../building/variables.md#buildx_bake_git_auth_token)
+- [`BUILDX_BAKE_GIT_AUTH_HEADER`](../building/variables.md#buildx_bake_git_auth_header)
+- [`BUILDX_BAKE_GIT_SSH`](../building/variables.md#buildx_bake_git_ssh)

content/build/building/variables.md

@@ -308,6 +308,9 @@ They're used to configure the Buildx client, or the BuildKit daemon.
 | [BUILDKIT_HOST](#buildkit_host)                                             | String            | Specify host to use for remote builders.             |
 | [BUILDKIT_PROGRESS](#buildkit_progress)                                     | String            | Configure type of progress output.                   |
 | [BUILDKIT_TTY_LOG_LINES](#buildkit_tty_log_lines)                           | String            | Number of log lines (for active steps in tty mode).  |
+| [BUILDX_BAKE_GIT_AUTH_HEADER](#buildx_bake_git_auth_header)                 | String            | HTTP authentication scheme for remote Bake files.    |
+| [BUILDX_BAKE_GIT_AUTH_TOKEN](#buildx_bake_git_auth_token)                   | String            | HTTP authentication token for remote Bake files.     |
+| [BUILDX_BAKE_GIT_SSH](#buildx_bake_git_ssh)                                 | String            | SSH authentication for remote Bake files.            |
 | [BUILDX_BUILDER](#buildx_builder)                                           | String            | Specify the builder instance to use.                 |
 | [BUILDX_CONFIG](#buildx_config)                                             | String            | Specify location for configuration, state, and logs. |
 | [BUILDX_EXPERIMENTAL](#buildx_experimental)                                 | Boolean           | Turn on experimental features.                       |
@@ -326,6 +329,8 @@ For example, `true`, `1`, and `T` all evaluate to true.
 Evaluation is done using the `strconv.ParseBool` function in the Go standard library.
 See the [reference documentation](https://pkg.go.dev/strconv#ParseBool) for details.
 
+<!-- vale Docker.HeadingSentenceCase = NO -->
+
 ### BUILDKIT_COLORS
 
 Changes the colors of the terminal output. Set `BUILDKIT_COLORS` to a CSV string
@@ -426,6 +431,53 @@ Example:
 }
 ```
 
+### BUILDX_BAKE_GIT_AUTH_HEADER
+
+{{< introduced buildx 0.14.0 >}}
+
+Sets the HTTP authentication scheme when using a remote Bake definition in a private Git repository.
+This is equivalent to the [`GIT_AUTH_HEADER` secret](./secrets#http-authentication-scheme),
+but facilitates the pre-flight authentication in Bake when loading the remote Bake file.
+Supported values are `bearer` (default) and `basic`.
+
+Usage:
+
+```console
+$ export BUILDX_BAKE_GIT_AUTH_HEADER=basic
+```
+
+### BUILDX_BAKE_GIT_AUTH_TOKEN
+
+{{< introduced buildx 0.14.0 >}}
+
+Sets the HTTP authentication token when using a remote Bake definition in a private Git repository.
+This is equivalent to the [`GIT_AUTH_TOKEN` secret](./secrets#git-authentication-for-remote-contexts),
+but facilitates the pre-flight authentication in Bake when loading the remote Bake file.
+
+Usage:
+
+```console
+$ export BUILDX_BAKE_GIT_AUTH_TOKEN=$(cat git-token.txt)
+```
+
+### BUILDX_BAKE_GIT_SSH
+
+{{< introduced buildx 0.14.0 >}}
+
+Lets you specify a list of SSH agent socket filepaths to forward to Bake
+for authenticating to a Git server when using a remote Bake definition in a private repository.
+This is similar to SSH mounts for builds, but facilitates the pre-flight authentication in Bake when resolving the build definition.
+
+Setting this environment is typically not necessary, because Bake will use the `SSH_AUTH_SOCK` agent socket by default.
+You only need to specify this variable if you want to use a socket with a different filepath.
+This variable can take multiple paths using a comma-separated string.
+
+Usage:
+
+```console
+$ export BUILDX_BAKE_GIT_SSH=/run/foo/listener.sock,~/.creds/ssh.sock
+```
+
 ### BUILDX_BUILDER
 
 Overrides the configured builder instance. Same as the `docker buildx --builder`
@@ -545,3 +597,4 @@ Usage:
 $ export BUILDX_NO_DEFAULT_LOAD=1
 ```
 
+<!-- vale Docker.HeadingSentenceCase = YES -->