diff --git a/src/Auth/ApiMandatoryHeadersMiddleware.php b/src/Auth/ApiMandatoryHeadersMiddleware.php
new file mode 100644
index 0000000..16bdecb
--- /dev/null
+++ b/src/Auth/ApiMandatoryHeadersMiddleware.php
@@ -0,0 +1,177 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Uwil\ArcadiaApiPhpClient\Auth;
+
+use GuzzleHttp\Promise\PromiseInterface;
+use GuzzleHttp\Psr7\Utils;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\UriInterface as Uri;
+use Ramsey\Uuid\Uuid;
+use Uwil\ArcadiaApiPhpClient\Lib\LibMiddleware;
+
+/**
+ * @internal
+ */
+final class ApiMandatoryHeadersMiddleware implements LibMiddleware
+{
+    public const string HANDLER_NAME = 'Arcadia API request Signature';
+
+    private const string SHA256_EMPTY_STRING_HASH = 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855';
+
+    public const string HEADER_CLIENT_IDENTIFIER = 'X-Client-Identifier';
+
+    public const string HEADER_BODY_HASH = 'X-Body-Hash';
+
+    public const string HEADER_TIMESTAMP = 'X-Timestamp';
+
+    public const string HEADER_SIGNATURE = 'X-Signature';
+
+    public const string HEADER_NONCE = 'X-Nonce';
+
+    /**
+     * This middleware signs the request using AWS-style signatures.
+     */
+    public static function signRequest(
+        ClientIdentifier $apiKey,
+        ClientSecret $withSecret,
+    ): callable {
+        return static function (callable $handler) use ($apiKey, $withSecret): self {
+            return new self($handler, $apiKey, $withSecret);
+        };
+    }
+
+    /**
+     * @param  callable(RequestInterface, array<string, mixed>): PromiseInterface  $nextHandler  Next handler to invoke.
+     */
+    public function __construct(
+        private $nextHandler,
+        private ClientIdentifier $apiKey,
+        private ClientSecret $withSecret
+    ) {
+    }
+
+    /** @param array<string, mixed> $options */
+    public function __invoke(RequestInterface $request, array $options): PromiseInterface
+    {
+        $fn = $this->nextHandler;
+
+        $signedRequest = $this->sign($request);
+
+        return $fn($signedRequest, $options);
+    }
+
+    private function sign(RequestInterface $request): RequestInterface
+    {
+        /** @var array<string,string> $modifyMap */
+        $modifyMap = [];
+
+        $this->addClientIdHeader($request, $modifyMap);
+        $this->addTimestampHeader($request, $modifyMap);
+        $this->addNonceHeader($request, $modifyMap);
+        $this->addBodyHashHeader($request, $modifyMap);
+        $this->addSignatureHeader($request, $modifyMap, $this->withSecret);
+
+        return Utils::modifyRequest($request, [
+            'set_headers' => $modifyMap,
+        ]);
+    }
+
+    /** @param array<string,string> $modifyMap */
+    private function addClientIdHeader(RequestInterface $request, array &$modifyMap): void
+    {
+        if (! $request->hasHeader(self::HEADER_CLIENT_IDENTIFIER)) {
+            $modifyMap[self::HEADER_CLIENT_IDENTIFIER] = $this->apiKey->value;
+        }
+    }
+
+    /** @param array<string,string> $modifyMap */
+    private function addTimestampHeader(RequestInterface $request, array &$modifyMap): void
+    {
+        if (! $request->hasHeader(self::HEADER_TIMESTAMP)) {
+            $modifyMap[self::HEADER_TIMESTAMP] = (new \DateTimeImmutable('now', new \DateTimeZone('UTC')))->format(\DateTimeInterface::ATOM);
+        }
+    }
+
+    /** @param array<string,string> $modifyMap */
+    private function addNonceHeader(RequestInterface $request, array &$modifyMap): void
+    {
+        if (! $request->hasHeader(self::HEADER_NONCE)) {
+            $modifyMap[self::HEADER_NONCE] = $this->generateNonce()->value->toString();
+        }
+    }
+
+    /** @param array<string,string> $modifyMap */
+    private function addBodyHashHeader(RequestInterface $request, array &$modifyMap): void
+    {
+        if (! $request->hasHeader(self::HEADER_BODY_HASH)) {
+            $body = $request->getBody();
+            $body->rewind();
+            $hash                              = hash('sha256', $body->getContents());
+            $modifyMap[self::HEADER_BODY_HASH] = $hash;
+        }
+    }
+
+    /** @param array<string,string> $modifyMap */
+    private function addSignatureHeader(
+        RequestInterface $request,
+        array &$modifyMap,
+        ClientSecret $withSecret
+    ): void {
+        $signaturePayload                  = $this->compileDataToSign($request, $modifyMap);
+        $signature                         = $this->calculateSignature($signaturePayload, $withSecret);
+        $modifyMap[self::HEADER_SIGNATURE] = $signature;
+    }
+
+    /** @param list<string> $signaturePayload */
+    private function calculateSignature(array $signaturePayload, ClientSecret $withSecret): string
+    {
+        $payloadString = implode('|', $signaturePayload);
+
+        return hash_hmac('sha256', $payloadString, $withSecret->value);
+    }
+
+    /**
+     * @param  array<string,string>  $modifyMap
+     * @return list<string>
+     */
+    private function compileDataToSign(RequestInterface $request, array $modifyMap): array
+    {
+        $timestamp = $modifyMap[self::HEADER_TIMESTAMP] ?? $request->getHeaderLine(self::HEADER_TIMESTAMP);
+        $nonce     = $modifyMap[self::HEADER_NONCE]     ?? $request->getHeaderLine(self::HEADER_NONCE);
+        $bodyHash  = $modifyMap[self::HEADER_BODY_HASH] ?? ($request->getHeaderLine(self::HEADER_BODY_HASH) ?: self::SHA256_EMPTY_STRING_HASH);
+
+        return [
+            strtoupper($request->getMethod()),
+            $this->getOrdonatedPathAndQuery($request->getUri()),
+            $timestamp,
+            $nonce,
+            $bodyHash,
+        ];
+    }
+
+    private function getOrdonatedPathAndQuery(Uri $fromUri): string
+    {
+        $path  = $fromUri->getPath();
+        $query = $fromUri->getQuery();
+
+        if ($query === '') {
+            return $path;
+        }
+
+        // NOTE: Sort query parameters to ensure consistent signature generation
+        parse_str($query, $queryParams);
+        ksort($queryParams);
+        $sortedQuery = http_build_query($queryParams);
+
+        return "{$path}?{$sortedQuery}";
+    }
+
+    private function generateNonce(): Nonce
+    {
+        return new Nonce(
+            value: Uuid::uuid7(),
+        );
+    }
+}
diff --git a/src/Auth/ClientIdentifier.php b/src/Auth/ClientIdentifier.php
new file mode 100644
index 0000000..4de473a
--- /dev/null
+++ b/src/Auth/ClientIdentifier.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Uwil\ArcadiaApiPhpClient\Auth;
+
+final readonly class ClientIdentifier
+{
+    public function __construct(
+        #[\SensitiveParameter]
+        public string $value,
+    ) {
+        if (empty(mb_trim($value))) {
+            throw new \InvalidArgumentException('ClientIdentifier cannot be empty.');
+        }
+    }
+}
diff --git a/src/Auth/ClientSecret.php b/src/Auth/ClientSecret.php
new file mode 100644
index 0000000..17eb0a5
--- /dev/null
+++ b/src/Auth/ClientSecret.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Uwil\ArcadiaApiPhpClient\Auth;
+
+final readonly class ClientSecret
+{
+    public function __construct(
+        #[\SensitiveParameter]
+        public string $value,
+    ) {
+        if (empty(mb_trim($value))) {
+            throw new \InvalidArgumentException('ClientSecret cannot be empty.');
+        }
+    }
+}
diff --git a/src/Auth/Nonce.php b/src/Auth/Nonce.php
new file mode 100644
index 0000000..3595e4a
--- /dev/null
+++ b/src/Auth/Nonce.php
@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Uwil\ArcadiaApiPhpClient\Auth;
+
+use Ramsey\Uuid\Uuid;
+use Ramsey\Uuid\UuidInterface;
+
+final readonly class Nonce
+{
+    public function __construct(
+        public readonly UuidInterface $value,
+    ) {
+        if (! Uuid::isValid($value->toString())) {
+            throw new \InvalidArgumentException('Nonce value is not a valid UUID');
+        }
+    }
+}