cli/command/container: --use-api-socket: support DOCKER_AUTH_CONFIG

With this patch, the `--use-api-socket` flag can obtain credentials from
a validly formatted `DOCKER_AUTH_CONFIG` environment-variable. If the
env-var is not set, or doesn't contain credentials, it falls back to
attempting to read credentials from the CLI's configured credentials
store.

With this patch:

    # Make sure there's no auth on disk first
    mkdir -p tmpConfig
    export DOCKER_CONFIG=$PWD/tmpConfig
    rm -f $PWD/tmpConfig/config.json

    # no credentials
    docker run --rm --use-api-socket alpine cat /run/secrets/docker/config.json
    cat: can't open '/run/secrets/docker/config.json': No such file or directory

    # pass credentials through DOCKER_AUTH_CONFIG
    DOCKER_AUTH_CONFIG='{"auths": {"https://index.docker.io/v1/": {"auth": "am9lam9lOmhlbGxv"}}}' docker run --rm --use-api-socket alpine cat /run/secrets/docker/config.json
    {
        "auths": {
            "https://index.docker.io/v1/": {
                "auth": "am9lam9lOmhlbGxv"
            }
        }
    }

    # credentials from file if no DOCKER_AUTH_CONFIG is set
    echo '{"auths": {"https://index.docker.io/v1/": {"auth": "am9lam9lOmhlbGxv"}}}' > "${DOCKER_CONFIG}/config.json"
    docker run --rm --use-api-socket alpine cat /run/secrets/docker/config.json
    {
        "auths": {
            "https://index.docker.io/v1/": {
                "auth": "am9lam9lOmhlbGxv"
            }
        }
    }

    # same if DOCKER_AUTH_CONFIG is set, but doesn't contain credentials
    DOCKER_AUTH_CONFIG='{}' docker run --rm --use-api-socket alpine cat /run/secrets/docker/config.json
    {
        "auths": {
            "https://index.docker.io/v1/": {
                "auth": "am9lam9lOmhlbGxv"
            }
        }
    }

    DOCKER_AUTH_CONFIG='{"auths": {}}' docker run --rm --use-api-socket alpine cat /run/secrets/docker/config.json
    {
        "auths": {
            "https://index.docker.io/v1/": {
                "auth": "am9lam9lOmhlbGxv"
            }
        }
    }

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/container/auth_config_utils.go

@@ -0,0 +1,46 @@
+package container
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/docker/cli/cli/config"
+	"github.com/docker/cli/cli/config/configfile"
+	"github.com/docker/cli/cli/config/types"
+)
+
+// readCredentials resolves auth-config from the current environment to be
+// applied to the container if the `--use-api-socket` flag is set.
+//
+//   - If a valid "DOCKER_AUTH_CONFIG" env-var is found, and it contains
+//     credentials, it's value is used.
+//   - If no "DOCKER_AUTH_CONFIG" env-var is found, or it does not contain
+//     credentials, it attempts to read from the CLI's credentials store.
+//
+// It returns an error if either the "DOCKER_AUTH_CONFIG" is incorrectly
+// formatted, or when failing to read from the credentials store.
+//
+// A nil value is returned if neither option contained any credentials.
+func readCredentials(dockerCLI config.Provider) (creds map[string]types.AuthConfig, _ error) {
+	if v, ok := os.LookupEnv("DOCKER_AUTH_CONFIG"); ok && v != "" {
+		// The results are expected to have been unmarshaled the same as
+		// when reading from a config-file, which includes decoding the
+		// base64-encoded "username:password" into the "UserName" and
+		// "Password" fields.
+		ac := &configfile.ConfigFile{}
+		if err := ac.LoadFromReader(strings.NewReader(v)); err != nil {
+			return nil, fmt.Errorf("failed to read credentials from DOCKER_AUTH_CONFIG: %w", err)
+		}
+		if len(ac.AuthConfigs) > 0 {
+			return ac.AuthConfigs, nil
+		}
+	}
+
+	// Resolve this here for later, ensuring we error our before we create the container.
+	creds, err := dockerCLI.ConfigFile().GetAllCredentials()
+	if err != nil {
+		return nil, fmt.Errorf("resolving credentials failed: %w", err)
+	}
+	return creds, nil
+}

cli/command/container/create.go

@@ -295,7 +295,7 @@ func createContainer(ctx context.Context, dockerCli command.Cli, containerCfg *c
 		// what they're doing and don't inject the creds.
 		if !envvarPresent {
 			// Resolve this here for later, ensuring we error our before we create the container.
-			creds, err := dockerCli.ConfigFile().GetAllCredentials()
+			creds, err := readCredentials(dockerCli)
 			if err != nil {
 				return "", fmt.Errorf("resolving credentials failed: %w", err)
 			}