feat: run docker login

.golangci.yaml

@@ -16,6 +16,10 @@ linters:
     - structcheck
     - varcheck
 
+    # Linters that are not used for this project.
+    - wrapcheck
+    - depguard
+
 linters-settings:
   goheader:
     template: |-

docker/exec.go

@@ -0,0 +1,24 @@
+// Copyright Josh Komoroske. All rights reserved.
+// Use of this source code is governed by the MIT license,
+// a copy of which can be found in the LICENSE.txt file.
+// SPDX-License-Identifier: MIT
+
+// Package docker exposes functions for executing specific docker commands.
+package docker
+
+import (
+	"os"
+	"os/exec"
+	"strings"
+)
+
+// Login executes a docker login to ghcr.io with the given username and
+// password.
+func Login(username, password string) error {
+	cmd := exec.Command("/usr/bin/docker", "login", "ghcr.io", "-u", username, "--password-stdin")
+	cmd.Stdin = strings.NewReader(password + "\n")
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	return cmd.Run()
+}

main.go

@@ -9,6 +9,8 @@ package main
 import (
 	"fmt"
 	"os"
+
+	"github.com/joshdk/actions-docker-shim/docker"
 )
 
 func main() {
@@ -18,6 +20,26 @@ func main() {
 	}
 }
 
+//nolint:forbidigo,wsl
 func mainCmd() error {
+	var token string
+	if value := os.Getenv("GITHUB_TOKEN"); value != "" {
+		// Environment variable named "GITHUB_TOKEN".
+		token = value
+	} else if value := os.Getenv("INPUT_GITHUB_TOKEN"); value != "" {
+		// Input named "github-token".
+		token = value
+	} else if value := os.Getenv("INPUT_TOKEN"); value != "" {
+		// Input named "token".
+		token = value
+	}
+
+	fmt.Printf("::group::%s\n", "Docker login")
+	err := docker.Login(os.Getenv("GITHUB_ACTOR"), token)
+	fmt.Println("::endgroup::")
+	if err != nil {
+		return err
+	}
+
 	return nil
 }