diff --git a/composer.json b/composer.json
index 3542a07..43e1b56 100644
--- a/composer.json
+++ b/composer.json
@@ -28,7 +28,7 @@
     "require": {
         "php": "8.1.*||8.2.*||8.3.*",
         "ext-zip": "*",
-        "composer/composer": "^2.7",
+        "composer/composer": "dev-main@dev",
         "guzzlehttp/guzzle": "^7.8",
         "guzzlehttp/psr7": "^2.6",
         "illuminate/container": "^10.47",
diff --git a/composer.lock b/composer.lock
index e8d4935..1189dc7 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "694d5bf1b96fcceae6af19c03eb55095",
+    "content-hash": "fb31ac50e2d4c78585e5dc67fbef9477",
     "packages": [
         {
             "name": "composer/ca-bundle",
@@ -157,16 +157,16 @@
         },
         {
             "name": "composer/composer",
-            "version": "2.7.1",
+            "version": "dev-main",
             "source": {
                 "type": "git",
                 "url": "https://github.com/composer/composer.git",
-                "reference": "aaf6ed5ccd27c23f79a545e351b4d7842a99d0bc"
+                "reference": "b12a88b7f3313e9dbae5b58085323b8328d10296"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/composer/composer/zipball/aaf6ed5ccd27c23f79a545e351b4d7842a99d0bc",
-                "reference": "aaf6ed5ccd27c23f79a545e351b4d7842a99d0bc",
+                "url": "https://api.github.com/repos/composer/composer/zipball/b12a88b7f3313e9dbae5b58085323b8328d10296",
+                "reference": "b12a88b7f3313e9dbae5b58085323b8328d10296",
                 "shasum": ""
             },
             "require": {
@@ -205,6 +205,7 @@
                 "ext-zip": "Enabling the zip extension allows you to unzip archives",
                 "ext-zlib": "Allow gzip compression of HTTP requests"
             },
+            "default-branch": true,
             "bin": [
                 "bin/composer"
             ],
@@ -251,7 +252,7 @@
                 "irc": "ircs://irc.libera.chat:6697/composer",
                 "issues": "https://github.com/composer/composer/issues",
                 "security": "https://github.com/composer/composer/security/policy",
-                "source": "https://github.com/composer/composer/tree/2.7.1"
+                "source": "https://github.com/composer/composer/tree/main"
             },
             "funding": [
                 {
@@ -267,7 +268,7 @@
                     "type": "tidelift"
                 }
             ],
-            "time": "2024-02-09T14:26:28+00:00"
+            "time": "2024-03-22T08:29:43+00:00"
         },
         {
             "name": "composer/metadata-minifier",
@@ -5740,7 +5741,9 @@
     ],
     "aliases": [],
     "minimum-stability": "stable",
-    "stability-flags": [],
+    "stability-flags": {
+        "composer/composer": 20
+    },
     "prefer-stable": false,
     "prefer-lowest": false,
     "platform": {
diff --git a/src/Command/DownloadCommand.php b/src/Command/DownloadCommand.php
index 5f8cef2..9fe973a 100644
--- a/src/Command/DownloadCommand.php
+++ b/src/Command/DownloadCommand.php
@@ -8,10 +8,12 @@
 use InvalidArgumentException;
 use Php\Pie\DependencyResolver\DependencyResolver;
 use Php\Pie\Downloading\DownloadAndExtract;
+use Php\Pie\TargetPhp\PhpBinaryPath;
 use Symfony\Component\Console\Attribute\AsCommand;
 use Symfony\Component\Console\Command\Command;
 use Symfony\Component\Console\Input\InputArgument;
 use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Output\OutputInterface;
 use Webmozart\Assert\Assert;
 
@@ -30,6 +32,7 @@
 final class DownloadCommand extends Command
 {
     private const ARG_REQUESTED_PACKAGE_AND_VERSION = 'requested-package-and-version';
+    private const OPTION_WITH_PHP_CONFIG            = 'with-php-config';
 
     public function __construct(
         private readonly DependencyResolver $dependencyResolver,
@@ -47,18 +50,35 @@ public function configure(): void
             InputArgument::REQUIRED,
             'The extension name and version constraint to use, in the format {ext-name}{?:version-constraint}{?@dev-branch-name}, for example `ext-debug:^1.0`',
         );
+        $this->addOption(
+            self::OPTION_WITH_PHP_CONFIG,
+            null,
+            InputOption::VALUE_OPTIONAL,
+            'The path to `php-config` to use',
+        );
     }
 
     public function execute(InputInterface $input, OutputInterface $output): int
     {
+        $phpBinaryPath = PhpBinaryPath::fromCurrentProcess();
+
+        /** @var mixed $withPhpConfig */
+        $withPhpConfig = $input->getOption(self::OPTION_WITH_PHP_CONFIG);
+        if (is_string($withPhpConfig) && $withPhpConfig !== '') {
+            $phpBinaryPath = PhpBinaryPath::fromPhpConfigExecutable($withPhpConfig);
+        }
+
+        $output->writeln(sprintf('<info>You are running PHP %s</info>', PHP_VERSION));
+        $output->writeln(sprintf('<info>Target PHP installation: %s (from %s)</info>', $phpBinaryPath->version(), $phpBinaryPath->phpBinaryPath));
+
         $requestedNameAndVersionPair = $this->requestedNameAndVersionPair($input);
 
         $package = ($this->dependencyResolver)(
+            $phpBinaryPath,
             $requestedNameAndVersionPair['name'],
             $requestedNameAndVersionPair['version'],
         );
 
-        $output->writeln(sprintf('<info>You are running PHP %s</info>', PHP_VERSION));
         $output->writeln(sprintf('<info>Found package:</info> %s (version: %s)', $package->name, $package->version));
         $output->writeln(sprintf('<info>Dist download URL:</info> %s', $package->downloadUrl ?? '(none)'));
 
diff --git a/src/Container.php b/src/Container.php
index 73c6238..a84ce4c 100644
--- a/src/Container.php
+++ b/src/Container.php
@@ -8,10 +8,7 @@
 use Composer\Factory as ComposerFactory;
 use Composer\IO\ConsoleIO;
 use Composer\IO\IOInterface;
-use Composer\IO\NullIO;
 use Composer\Repository\CompositeRepository;
-use Composer\Repository\PlatformRepository;
-use Composer\Repository\RepositoryFactory;
 use Composer\Repository\RepositorySet;
 use Composer\Util\AuthHelper;
 use Composer\Util\Platform;
@@ -24,6 +21,7 @@
 use Php\Pie\Downloading\DownloadZip;
 use Php\Pie\Downloading\ExtractZip;
 use Php\Pie\Downloading\UnixDownloadAndExtract;
+use Php\Pie\TargetPhp\ResolveTargetPhpToPlatformRepository;
 use Psr\Container\ContainerInterface;
 use RuntimeException;
 use Symfony\Component\Console\Helper\HelperSet;
@@ -51,7 +49,7 @@ public static function factory(): ContainerInterface
         });
         $container->singleton(Composer::class, static function (ContainerInterface $container): Composer {
             $io       = $container->get(IOInterface::class);
-            $composer = ComposerFactory::create($io);
+            $composer = (new ComposerFactory())->createComposer($io, [], true);
             $io->loadConfiguration($composer->getConfig());
 
             return $composer;
@@ -59,13 +57,14 @@ public static function factory(): ContainerInterface
 
         $container->singleton(
             DependencyResolver::class,
-            static function (): DependencyResolver {
+            static function (ContainerInterface $container): DependencyResolver {
+                $composer      = $container->get(Composer::class);
                 $repositorySet = new RepositorySet();
-                $repositorySet->addRepository(new CompositeRepository(RepositoryFactory::defaultReposWithDefaultManager(new NullIO())));
+                $repositorySet->addRepository(new CompositeRepository($composer->getRepositoryManager()->getRepositories()));
 
                 return new ResolveDependencyWithComposer(
-                    new PlatformRepository(),
                     $repositorySet,
+                    new ResolveTargetPhpToPlatformRepository(),
                 );
             },
         );
diff --git a/src/DependencyResolver/DependencyResolver.php b/src/DependencyResolver/DependencyResolver.php
index 908888a..57a4316 100644
--- a/src/DependencyResolver/DependencyResolver.php
+++ b/src/DependencyResolver/DependencyResolver.php
@@ -4,9 +4,11 @@
 
 namespace Php\Pie\DependencyResolver;
 
+use Php\Pie\TargetPhp\PhpBinaryPath;
+
 /** @internal This is not public API for PIE, so should not be depended upon unless you accept the risk of BC breaks */
 interface DependencyResolver
 {
     /** @throws UnableToResolveRequirement */
-    public function __invoke(string $packageName, string|null $requestedVersion): Package;
+    public function __invoke(PhpBinaryPath $phpBinaryPath, string $packageName, string|null $requestedVersion): Package;
 }
diff --git a/src/DependencyResolver/ResolveDependencyWithComposer.php b/src/DependencyResolver/ResolveDependencyWithComposer.php
index 995b67e..f70c186 100644
--- a/src/DependencyResolver/ResolveDependencyWithComposer.php
+++ b/src/DependencyResolver/ResolveDependencyWithComposer.php
@@ -6,23 +6,29 @@
 
 use Composer\Package\CompletePackageInterface;
 use Composer\Package\Version\VersionSelector;
-use Composer\Repository\PlatformRepository;
 use Composer\Repository\RepositorySet;
+use Php\Pie\TargetPhp\PhpBinaryPath;
+use Php\Pie\TargetPhp\ResolveTargetPhpToPlatformRepository;
 
 /** @internal This is not public API for PIE, so should not be depended upon unless you accept the risk of BC breaks */
 final class ResolveDependencyWithComposer implements DependencyResolver
 {
     public function __construct(
-        private readonly PlatformRepository $platformRepository,
         private readonly RepositorySet $repositorySet,
+        private readonly ResolveTargetPhpToPlatformRepository $resolveTargetPhpToPlatformRepository,
     ) {
     }
 
-    public function __invoke(string $packageName, string|null $requestedVersion): Package
+    public function __invoke(PhpBinaryPath $phpBinaryPath, string $packageName, string|null $requestedVersion): Package
     {
-        $package = (new VersionSelector($this->repositorySet, $this->platformRepository))
+        $package = (new VersionSelector(
+            $this->repositorySet,
+            ($this->resolveTargetPhpToPlatformRepository)($phpBinaryPath),
+        ))
             ->findBestCandidate($packageName, $requestedVersion);
 
+        // @todo check it is a `php-ext` or `php-ext-zend`
+
         if (! $package instanceof CompletePackageInterface) {
             throw UnableToResolveRequirement::fromRequirement($packageName, $requestedVersion);
         }
diff --git a/src/TargetPhp/PhpBinaryPath.php b/src/TargetPhp/PhpBinaryPath.php
index d57aa5a..9d364c0 100644
--- a/src/TargetPhp/PhpBinaryPath.php
+++ b/src/TargetPhp/PhpBinaryPath.php
@@ -8,8 +8,10 @@
 use Symfony\Component\Process\Process;
 use Webmozart\Assert\Assert;
 
+use function trim;
+
 /** @internal This is not public API for PIE, so should not be depended upon unless you accept the risk of BC breaks */
-final class PhpBinaryPath
+class PhpBinaryPath
 {
     /** @param non-empty-string $phpBinaryPath */
     private function __construct(readonly string $phpBinaryPath)
@@ -22,6 +24,7 @@ public function version(): string
             ->mustRun()
             ->getOutput());
         Assert::stringNotEmpty($phpVersion, 'Could not determine PHP version');
+
         return $phpVersion;
     }
 
@@ -32,13 +35,15 @@ public static function fromPhpConfigExecutable(string $phpConfig): self
             ->mustRun()
             ->getOutput());
         Assert::stringNotEmpty($phpExecutable, 'Could not find path to PHP executable.');
+
         return new self($phpExecutable);
     }
 
     public static function fromCurrentProcess(): self
     {
-        $phpExecutable = trim((new PhpExecutableFinder())->find());
+        $phpExecutable = trim((string) (new PhpExecutableFinder())->find());
         Assert::stringNotEmpty($phpExecutable, 'Could not find path to PHP executable.');
+
         return new self($phpExecutable);
     }
 }
diff --git a/src/TargetPhp/ResolveTargetPhpToPlatformRepository.php b/src/TargetPhp/ResolveTargetPhpToPlatformRepository.php
new file mode 100644
index 0000000..9e3eaac
--- /dev/null
+++ b/src/TargetPhp/ResolveTargetPhpToPlatformRepository.php
@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Php\Pie\TargetPhp;
+
+use Composer\Repository\PlatformRepository;
+
+class ResolveTargetPhpToPlatformRepository
+{
+    public function __invoke(PhpBinaryPath $phpBinaryPath): PlatformRepository
+    {
+        // @todo I expect we also need to map the extensions for the given PHP binary, somehow?
+        return new PlatformRepository([], ['php' => $phpBinaryPath->version()]);
+    }
+}
diff --git a/test/integration/Command/DownloadCommandTest.php b/test/integration/Command/DownloadCommandTest.php
index 1261236..e58aa7e 100644
--- a/test/integration/Command/DownloadCommandTest.php
+++ b/test/integration/Command/DownloadCommandTest.php
@@ -26,13 +26,18 @@ public function setUp(): void
 
     public function testDownloadCommand(): void
     {
-        $this->commandTester->execute(['requested-package-and-version' => 'ramsey/uuid']);
+        if (PHP_VERSION_ID < 80300 || PHP_VERSION_ID >= 80400) {
+            self::markTestSkipped('This test can only run on PHP 8.3 - you are running ' . PHP_VERSION);
+        }
+
+        // 1.0.0 is only compatible with PHP 8.3.0
+        $this->commandTester->execute(['requested-package-and-version' => 'asgrim/example-pie-extension:1.0.0']);
 
         $this->commandTester->assertCommandIsSuccessful();
 
         $outputString = $this->commandTester->getDisplay();
-        self::assertStringContainsString('Found package: ramsey/uuid (version: ', $outputString);
-        self::assertStringContainsString('Dist download URL: https://api.github.com/repos/ramsey/uuid/zipball/', $outputString);
+        self::assertStringContainsString('Found package: asgrim/example-pie-extension (version: 1.0.0)', $outputString);
+        self::assertStringContainsString('Dist download URL: https://api.github.com/repos/asgrim/example-pie-extension/zipball/', $outputString);
     }
 
     public function testDownloadCommandFailsWhenUsingIncompatiblePhpVersion(): void
@@ -42,6 +47,7 @@ public function testDownloadCommandFailsWhenUsingIncompatiblePhpVersion(): void
         }
 
         $this->expectException(UnableToResolveRequirement::class);
-        $this->commandTester->execute(['requested-package-and-version' => 'phpunit/phpunit:^11.0']);
+        // 1.0.0 is only compatible with PHP 8.3.0
+        $this->commandTester->execute(['requested-package-and-version' => 'asgrim/example-pie-extension:1.0.0']);
     }
 }
diff --git a/test/unit/DependencyResolver/ResolveDependencyWithComposerTest.php b/test/unit/DependencyResolver/ResolveDependencyWithComposerTest.php
index 1aca5a1..0e24daa 100644
--- a/test/unit/DependencyResolver/ResolveDependencyWithComposerTest.php
+++ b/test/unit/DependencyResolver/ResolveDependencyWithComposerTest.php
@@ -6,11 +6,12 @@
 
 use Composer\IO\NullIO;
 use Composer\Repository\CompositeRepository;
-use Composer\Repository\PlatformRepository;
 use Composer\Repository\RepositoryFactory;
 use Composer\Repository\RepositorySet;
 use Php\Pie\DependencyResolver\ResolveDependencyWithComposer;
 use Php\Pie\DependencyResolver\UnableToResolveRequirement;
+use Php\Pie\TargetPhp\PhpBinaryPath;
+use Php\Pie\TargetPhp\ResolveTargetPhpToPlatformRepository;
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
@@ -19,6 +20,7 @@
 final class ResolveDependencyWithComposerTest extends TestCase
 {
     private RepositorySet $repositorySet;
+    private ResolveTargetPhpToPlatformRepository $resolveTargetPhpToPlatformRepository;
 
     public function setUp(): void
     {
@@ -26,14 +28,21 @@ public function setUp(): void
 
         $this->repositorySet = new RepositorySet();
         $this->repositorySet->addRepository(new CompositeRepository(RepositoryFactory::defaultReposWithDefaultManager(new NullIO())));
+
+        $this->resolveTargetPhpToPlatformRepository = new ResolveTargetPhpToPlatformRepository();
     }
 
     public function testPackageThatCanBeResolved(): void
     {
+        $phpBinaryPath = $this->createMock(PhpBinaryPath::class);
+        $phpBinaryPath->expects(self::once())
+            ->method('version')
+            ->willReturn('8.2.0');
+
         $package = (new ResolveDependencyWithComposer(
-            new PlatformRepository([], ['php' => '8.2.0']),
             $this->repositorySet,
-        ))('phpunit/phpunit', '^11.0');
+            $this->resolveTargetPhpToPlatformRepository,
+        ))($phpBinaryPath, 'phpunit/phpunit', '^11.0');
 
         self::assertSame('phpunit/phpunit', $package->name);
     }
@@ -55,12 +64,18 @@ public static function unresolvableDependencies(): array
     #[DataProvider('unresolvableDependencies')]
     public function testPackageThatCannotBeResolvedThrowsException(array $platformOverrides, string $package, string $version): void
     {
+        $phpBinaryPath = $this->createMock(PhpBinaryPath::class);
+        $phpBinaryPath->expects(self::once())
+            ->method('version')
+            ->willReturn($platformOverrides['php']);
+
         $this->expectException(UnableToResolveRequirement::class);
 
         (new ResolveDependencyWithComposer(
-            new PlatformRepository([], $platformOverrides),
             $this->repositorySet,
+            $this->resolveTargetPhpToPlatformRepository,
         ))(
+            $phpBinaryPath,
             $package,
             $version,
         );
diff --git a/test/unit/TargetPhp/PhpBinaryPathTest.php b/test/unit/TargetPhp/PhpBinaryPathTest.php
index b59fead..05c7551 100644
--- a/test/unit/TargetPhp/PhpBinaryPathTest.php
+++ b/test/unit/TargetPhp/PhpBinaryPathTest.php
@@ -8,6 +8,8 @@
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\TestCase;
 
+use const PHP_VERSION;
+
 #[CoversClass(PhpBinaryPath::class)]
 final class PhpBinaryPathTest extends TestCase
 {