diff --git a/src/Argument.php b/src/Argument.php
new file mode 100644
index 0000000..8272d3f
--- /dev/null
+++ b/src/Argument.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Kiboko\Component\Dockerfile;
+
+final readonly class Argument implements Variable
+{
+    public function __construct(
+        public string $name,
+    ) {
+    }
+
+    public function __toString()
+    {
+        return "\${{$this->name}}";
+    }
+}
diff --git a/src/Dockerfile.php b/src/Dockerfile.php
index 6b7b786..6308ad4 100644
--- a/src/Dockerfile.php
+++ b/src/Dockerfile.php
@@ -12,12 +12,12 @@ final class Dockerfile implements \IteratorAggregate, \Countable, FileInterface,
     /** @var iterable|Dockerfile\LayerInterface[] */
     private iterable $layers;
 
-    public function __construct(null|Dockerfile\LayerInterface ...$layers)
+    public function __construct(null|LayerInterface ...$layers)
     {
         $this->layers = $layers;
     }
 
-    public function push(Dockerfile\LayerInterface ...$layers): void
+    public function push(LayerInterface ...$layers): void
     {
         array_push($this->layers, ...$layers);
     }
diff --git a/src/Dockerfile/Arg.php b/src/Dockerfile/Arg.php
new file mode 100644
index 0000000..186cabc
--- /dev/null
+++ b/src/Dockerfile/Arg.php
@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Kiboko\Component\Dockerfile\Dockerfile;
+
+final readonly class Arg implements LayerInterface, \Stringable
+{
+    public function __construct(
+        private string $name,
+        private ?string $defaultValue = null,
+    ) {
+    }
+
+    public function __toString(): string
+    {
+        if (null !== $this->defaultValue) {
+            return sprintf('ARG %s=%s', $this->name, $this->defaultValue);
+        }
+
+        return sprintf('ARG %s', $this->name);
+    }
+}
diff --git a/src/EnvironmentVariable.php b/src/EnvironmentVariable.php
new file mode 100644
index 0000000..711a11f
--- /dev/null
+++ b/src/EnvironmentVariable.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Kiboko\Component\Dockerfile;
+
+final readonly class EnvironmentVariable implements Variable
+{
+    public function __construct(
+        public string $name,
+    ) {
+    }
+
+    public function __toString()
+    {
+        return "\${{$this->name}}";
+    }
+}
diff --git a/src/PHP/ComposerGlobalConfig.php b/src/PHP/ComposerGlobalConfig.php
new file mode 100644
index 0000000..7e87f38
--- /dev/null
+++ b/src/PHP/ComposerGlobalConfig.php
@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Kiboko\Component\Dockerfile\PHP;
+
+use Kiboko\Component\Dockerfile\Dockerfile;
+use Kiboko\Component\Dockerfile\Variable;
+
+final readonly class ComposerGlobalConfig implements Dockerfile\LayerInterface, \Stringable
+{
+    public function __construct(
+        private string $key,
+        private string|Variable $value,
+    ) {
+    }
+
+    public function __toString(): string
+    {
+        return (string) new Dockerfile\Run(<<<"RUN"
+            composer config --global {$this->key} {$this->value}
+            RUN
+        );
+    }
+}
diff --git a/src/PHP/ComposerGlobalGithubAuthentication.php b/src/PHP/ComposerGlobalGithubAuthentication.php
new file mode 100644
index 0000000..a50ccf4
--- /dev/null
+++ b/src/PHP/ComposerGlobalGithubAuthentication.php
@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Kiboko\Component\Dockerfile\PHP;
+
+use Kiboko\Component\Dockerfile\Dockerfile;
+use Kiboko\Component\Dockerfile\Variable;
+
+final readonly class ComposerGlobalGithubAuthentication implements Dockerfile\LayerInterface, \Stringable
+{
+    public function __construct(
+        private Variable $tokenArgument,
+        private string $host = 'github.com',
+    ) {
+    }
+
+    public function __toString(): string
+    {
+        return (string) new Dockerfile\Run(<<<"RUN"
+            composer config --global github-oauth.{$this->host} {$this->tokenArgument}
+            RUN,
+        );
+    }
+}
diff --git a/src/Variable.php b/src/Variable.php
new file mode 100644
index 0000000..4bcd9e9
--- /dev/null
+++ b/src/Variable.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Kiboko\Component\Dockerfile;
+
+interface Variable extends \Stringable
+{
+}