diff --git a/src/Application/Security/Events/ClientSecretGenerated.php b/src/Application/Security/Events/ClientSecretGenerated.php
new file mode 100644
index 0000000..6c01b8a
--- /dev/null
+++ b/src/Application/Security/Events/ClientSecretGenerated.php
@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Events;
+
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Shared\DDD\Event\Event;
+
+final readonly class ClientSecretGenerated implements Event
+{
+    public function __construct(
+        public ClientId $clientId,
+        public ClientIdentifier $clientIdentifier,
+        public \DateTimeImmutable $generatedAt,
+    ) {
+    }
+}
diff --git a/src/Application/Security/Events/ClientSecretRegenerated.php b/src/Application/Security/Events/ClientSecretRegenerated.php
new file mode 100644
index 0000000..04c040c
--- /dev/null
+++ b/src/Application/Security/Events/ClientSecretRegenerated.php
@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Events;
+
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Shared\DDD\Event\Event;
+
+final readonly class ClientSecretRegenerated implements Event
+{
+    public function __construct(
+        public ClientId $clientId,
+        public ClientIdentifier $clientIdentifier,
+        public \DateTimeImmutable $generatedAt,
+    ) {
+    }
+}
diff --git a/src/Application/Security/Events/ClientStatusToggled.php b/src/Application/Security/Events/ClientStatusToggled.php
new file mode 100644
index 0000000..ccd54f9
--- /dev/null
+++ b/src/Application/Security/Events/ClientStatusToggled.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Events;
+
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Shared\DDD\Event\Event;
+
+final readonly class ClientStatusToggled implements Event
+{
+    public function __construct(
+        public ClientId $clientId,
+        public ClientIdentifier $clientIdentifier,
+        public bool $isActive,
+        public \DateTimeImmutable $toggledAt,
+    ) {
+    }
+}
diff --git a/src/Application/Security/Exceptions/AuthenticationException.php b/src/Application/Security/Exceptions/AuthenticationException.php
new file mode 100644
index 0000000..41b8f14
--- /dev/null
+++ b/src/Application/Security/Exceptions/AuthenticationException.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Exceptions;
+
+use Shared\DDD\Exception\SecurityException;
+
+final class AuthenticationException extends SecurityException
+{
+    public function __construct()
+    {
+        parent::__construct('Authentication failed.');
+    }
+}
diff --git a/src/Application/Security/Exceptions/ClientNotFoundException.php b/src/Application/Security/Exceptions/ClientNotFoundException.php
new file mode 100644
index 0000000..d4dd1ac
--- /dev/null
+++ b/src/Application/Security/Exceptions/ClientNotFoundException.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Exceptions;
+
+use Shared\DDD\Exception\NotFoundException;
+
+final class ClientNotFoundException extends NotFoundException
+{
+    public static function forClient(string $clientId): self
+    {
+        return new self("Client '{$clientId}' not found.");
+    }
+}
diff --git a/src/Application/Security/Models/Entities/Client.php b/src/Application/Security/Models/Entities/Client.php
new file mode 100644
index 0000000..bc092ed
--- /dev/null
+++ b/src/Application/Security/Models/Entities/Client.php
@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Models\Entities;
+
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\ClientName;
+use Application\Security\Models\ValueObjects\ClientSecret;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Shared\DDD\Model\Entity;
+
+/**
+ * @implements Entity<ClientId>
+ */
+final class Client implements Entity
+{
+    private function __construct(
+        public ClientId $id,
+        public ClientIdentifier $identifier,
+        public ClientName $name,
+        public ClientSecret $secret,
+        public bool $isActive,
+        public \DateTimeInterface $createdAt,
+        public \DateTimeInterface $updatedAt,
+    ) {
+    }
+
+    #[\Override]
+    public function id(): ClientId
+    {
+        return $this->id;
+    }
+
+    public static function create(
+        ClientId $id,
+        ClientName $name,
+        ClientIdentifier $identifier,
+        ClientSecret $secret,
+    ): self {
+        $now = new \DateTimeImmutable();
+
+        return new self(
+            id: $id,
+            identifier: $identifier,
+            name: $name,
+            secret: $secret,
+            isActive: true,
+            createdAt: $now,
+            updatedAt: $now,
+        );
+    }
+
+    public static function hydrate(
+        ClientId $id,
+        ClientName $name,
+        ClientIdentifier $identifier,
+        ClientSecret $secret,
+        bool $isActive,
+        \DateTimeInterface $createdAt,
+        \DateTimeInterface $updatedAt,
+    ): self {
+        return new self(
+            id: $id,
+            identifier: $identifier,
+            name: $name,
+            secret: $secret,
+            isActive: $isActive,
+            createdAt: $createdAt,
+            updatedAt: $updatedAt,
+        );
+    }
+
+    public function regenerateSecret(ClientSecret $newSecret): void
+    {
+        $this->secret    = $newSecret;
+        $this->updatedAt = new \DateTimeImmutable();
+    }
+
+    public function toggleStatus(): bool
+    {
+        $this->isActive  = ! $this->isActive;
+        $this->updatedAt = new \DateTimeImmutable();
+
+        return $this->isActive;
+    }
+}
diff --git a/src/Application/Security/Models/ValueObjects/ClientIdentifier.php b/src/Application/Security/Models/ValueObjects/ClientIdentifier.php
new file mode 100644
index 0000000..4536bcd
--- /dev/null
+++ b/src/Application/Security/Models/ValueObjects/ClientIdentifier.php
@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Models\ValueObjects;
+
+use Shared\DDD\Security\UserIdentifier;
+
+final readonly class ClientIdentifier implements UserIdentifier
+{
+    public function __construct(
+        #[\SensitiveParameter]
+        public string $value,
+    ) {
+        if (empty(trim($value))) {
+            throw new \InvalidArgumentException('ClientIdentifier cannot be empty.');
+        }
+        if (! preg_match('/^[a-zA-Z0-9_-]+$/', $value)) {
+            throw new \InvalidArgumentException('ClientIdentifier can only contain alphanumeric characters, dashes, and underscores.');
+        }
+        if (strlen($value) < 43) {
+            throw new \InvalidArgumentException('ClientIdentifier must be at least 43 characters long.');
+        }
+        if (strlen($value) > 255) {
+            throw new \InvalidArgumentException('ClientIdentifier cannot exceed 255 characters.');
+        }
+    }
+
+    #[\Override]
+    public function value(): string
+    {
+        return $this->value;
+    }
+
+    #[\Override]
+    public function equals(mixed $other): bool
+    {
+        return $other instanceof self && $this->value === $other->value;
+    }
+}
diff --git a/src/Application/Security/Models/ValueObjects/ClientName.php b/src/Application/Security/Models/ValueObjects/ClientName.php
new file mode 100644
index 0000000..7f1627f
--- /dev/null
+++ b/src/Application/Security/Models/ValueObjects/ClientName.php
@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Models\ValueObjects;
+
+final readonly class ClientName
+{
+    public function __construct(
+        public readonly string $value,
+    ) {
+        if ($value === '') {
+            throw new \InvalidArgumentException('ClientName cannot be empty.');
+        }
+        if (strlen($value) > 255) {
+            throw new \InvalidArgumentException('ClientName cannot exceed 255 characters.');
+        }
+    }
+}
diff --git a/src/Application/Security/Models/ValueObjects/ClientSecret.php b/src/Application/Security/Models/ValueObjects/ClientSecret.php
new file mode 100644
index 0000000..1a03201
--- /dev/null
+++ b/src/Application/Security/Models/ValueObjects/ClientSecret.php
@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Models\ValueObjects;
+
+final readonly class ClientSecret
+{
+    public function __construct(
+        #[\SensitiveParameter]
+        public string $value,
+    ) {
+        if (empty(trim($value))) {
+            throw new \InvalidArgumentException('ClientSecret cannot be empty.');
+        }
+        if (! preg_match('/^[a-zA-Z0-9_-]+$/', $value)) {
+            throw new \InvalidArgumentException('ClientSecret can only contain alphanumeric characters, dashes, and underscores.');
+        }
+        if (strlen($value) < 86 || strlen($value) > 120) {
+            throw new \InvalidArgumentException('ClientSecret must be between 86 and 120 characters long.');
+        }
+    }
+}
diff --git a/src/Application/Security/Models/ValueObjects/Entities/ClientId.php b/src/Application/Security/Models/ValueObjects/Entities/ClientId.php
new file mode 100644
index 0000000..a755fe5
--- /dev/null
+++ b/src/Application/Security/Models/ValueObjects/Entities/ClientId.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Models\ValueObjects\Entities;
+
+use Ramsey\Uuid\UuidInterface;
+use Shared\DDD\Model\EntityId;
+use Shared\Helpers\Exceptions\InvalidUuidException;
+use Shared\Helpers\UuidHelper;
+
+final readonly class ClientId extends EntityId
+{
+    public function __construct(
+        public readonly UuidInterface $identifier,
+    ) {
+        if (UuidHelper::isV7($identifier) === false) {
+            throw InvalidUuidException::forValue($identifier->toString());
+        }
+        parent::__construct($identifier->toString());
+    }
+}
diff --git a/src/Application/Security/Models/ValueObjects/Request/HttpBodyHash.php b/src/Application/Security/Models/ValueObjects/Request/HttpBodyHash.php
new file mode 100644
index 0000000..9ed4c51
--- /dev/null
+++ b/src/Application/Security/Models/ValueObjects/Request/HttpBodyHash.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Models\ValueObjects\Request;
+
+final readonly class HttpBodyHash
+{
+    public function __construct(
+        #[\SensitiveParameter]
+        public string $value
+    ) {
+        if ($value === '') {
+            throw new \InvalidArgumentException('HttpBody cannot be empty');
+        }
+        // NOTE: Check if the body is a valid SHA256 hash (64 hex characters).
+        if (! preg_match('/^[a-f0-9]{64}$/i', $value)) {
+            throw new \InvalidArgumentException('HttpBody must be a valid SHA256 hash');
+        }
+    }
+}
diff --git a/src/Application/Security/Models/ValueObjects/Request/HttpMethod.php b/src/Application/Security/Models/ValueObjects/Request/HttpMethod.php
new file mode 100644
index 0000000..87fac0f
--- /dev/null
+++ b/src/Application/Security/Models/ValueObjects/Request/HttpMethod.php
@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Models\ValueObjects\Request;
+
+enum HttpMethod: string
+{
+    case GET     = 'GET';
+    case POST    = 'POST';
+    case PUT     = 'PUT';
+    case DELETE  = 'DELETE';
+    case PATCH   = 'PATCH';
+    case HEAD    = 'HEAD';
+    case OPTIONS = 'OPTIONS';
+}
diff --git a/src/Application/Security/Models/ValueObjects/Request/Nonce.php b/src/Application/Security/Models/ValueObjects/Request/Nonce.php
new file mode 100644
index 0000000..291895b
--- /dev/null
+++ b/src/Application/Security/Models/ValueObjects/Request/Nonce.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Models\ValueObjects\Request;
+
+use Ramsey\Uuid\UuidInterface;
+use Shared\Helpers\UuidHelper;
+
+final readonly class Nonce
+{
+    public function __construct(
+        public readonly UuidInterface $value,
+    ) {
+        UuidHelper::validateUuid($value);
+    }
+}
diff --git a/src/Application/Security/Models/ValueObjects/Request/Request.php b/src/Application/Security/Models/ValueObjects/Request/Request.php
new file mode 100644
index 0000000..7ded060
--- /dev/null
+++ b/src/Application/Security/Models/ValueObjects/Request/Request.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Models\ValueObjects\Request;
+
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Uri\Rfc3986\Uri;
+
+final readonly class Request
+{
+    public function __construct(
+        public readonly Uri $uri,
+        public readonly HttpMethod $method,
+        public readonly ?HttpBodyHash $bodyHash,
+        public readonly RequestSignature $signature,
+        public readonly Nonce $nonce,
+        public readonly ClientIdentifier $identifier,
+        public readonly RequestTimestamp $timestamp
+    ) {
+    }
+}
diff --git a/src/Application/Security/Models/ValueObjects/Request/RequestSignature.php b/src/Application/Security/Models/ValueObjects/Request/RequestSignature.php
new file mode 100644
index 0000000..2c9752c
--- /dev/null
+++ b/src/Application/Security/Models/ValueObjects/Request/RequestSignature.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Models\ValueObjects\Request;
+
+final readonly class RequestSignature
+{
+    public function __construct(
+        #[\SensitiveParameter]
+        public readonly string $value,
+    ) {
+        if (empty(trim($value))) {
+            throw new \InvalidArgumentException('RequestSignature cannot be empty.');
+        }
+
+        if (! preg_match('/^[0-9a-fA-F]{64}$/', $value)) {
+            throw new \InvalidArgumentException('RequestSignature must be a valid 64-character hex HMAC-SHA256 string.');
+        }
+    }
+}
diff --git a/src/Application/Security/Models/ValueObjects/Request/RequestTimestamp.php b/src/Application/Security/Models/ValueObjects/Request/RequestTimestamp.php
new file mode 100644
index 0000000..2dea1fc
--- /dev/null
+++ b/src/Application/Security/Models/ValueObjects/Request/RequestTimestamp.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Models\ValueObjects\Request;
+
+final readonly class RequestTimestamp
+{
+    public function __construct(
+        public \DateTimeImmutable $value
+    ) {
+    }
+}
diff --git a/src/Application/Security/Ports/Repositories/ClientRepository.php b/src/Application/Security/Ports/Repositories/ClientRepository.php
new file mode 100644
index 0000000..d1e5acb
--- /dev/null
+++ b/src/Application/Security/Ports/Repositories/ClientRepository.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Ports\Repositories;
+
+use Application\Security\Models\Entities\Client;
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Shared\DDD\Port\Repository;
+use Shared\Paginated;
+use Shared\Pagination;
+
+/**
+ * @extends Repository<ClientId, Client>
+ */
+interface ClientRepository extends Repository
+{
+    public function find(ClientId $id): ?Client;
+
+    public function persist(Client $client): void;
+
+    public function delete(Client $client): void;
+
+    public function findByIdentifier(ClientIdentifier $identifier): ?Client;
+
+    /** @return Paginated<Client> */
+    public function findAll(Pagination $pagination): Paginated;
+}
diff --git a/src/Application/Security/Ports/Services/ClientCredentialGenerator.php b/src/Application/Security/Ports/Services/ClientCredentialGenerator.php
new file mode 100644
index 0000000..69b2bc1
--- /dev/null
+++ b/src/Application/Security/Ports/Services/ClientCredentialGenerator.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Ports\Services;
+
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\ClientSecret;
+
+interface ClientCredentialGenerator
+{
+    public function generateIdentifier(): ClientIdentifier;
+
+    public function generateSecret(): ClientSecret;
+}
diff --git a/src/Application/Security/Ports/Services/HmacSignatureValidator.php b/src/Application/Security/Ports/Services/HmacSignatureValidator.php
new file mode 100644
index 0000000..6efa39f
--- /dev/null
+++ b/src/Application/Security/Ports/Services/HmacSignatureValidator.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Ports\Services;
+
+use Application\Security\Models\ValueObjects\ClientSecret;
+use Application\Security\Models\ValueObjects\Request\Request;
+
+interface HmacSignatureValidator
+{
+    public function validate(Request $request, ClientSecret $withSecret): bool;
+}
diff --git a/src/Application/Security/Ports/Services/NonceValidator.php b/src/Application/Security/Ports/Services/NonceValidator.php
new file mode 100644
index 0000000..fd05167
--- /dev/null
+++ b/src/Application/Security/Ports/Services/NonceValidator.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Ports\Services;
+
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\Request\Nonce;
+
+interface NonceValidator
+{
+    public function validateAndConsume(Nonce $nonce, ClientIdentifier $forClientIdentifier): bool;
+}
diff --git a/src/Application/Security/Ports/Services/RequestValidation/RequestValidationResult.php b/src/Application/Security/Ports/Services/RequestValidation/RequestValidationResult.php
new file mode 100644
index 0000000..74278d4
--- /dev/null
+++ b/src/Application/Security/Ports/Services/RequestValidation/RequestValidationResult.php
@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Ports\Services\RequestValidation;
+
+use Application\Security\Models\Entities\Client;
+
+final readonly class RequestValidationResult
+{
+    private function __construct(
+        public RequestValidationStatus $status,
+        public ?Client $client = null,
+    ) {
+    }
+
+    public static function valid(Client $client): self
+    {
+        return new self(RequestValidationStatus::VALID, $client);
+    }
+
+    public static function failed(RequestValidationStatus $reason): self
+    {
+        return new self($reason);
+    }
+
+    public function isValid(): bool
+    {
+        return $this->status === RequestValidationStatus::VALID;
+    }
+}
diff --git a/src/Application/Security/Ports/Services/RequestValidation/RequestValidationStatus.php b/src/Application/Security/Ports/Services/RequestValidation/RequestValidationStatus.php
new file mode 100644
index 0000000..ea5a392
--- /dev/null
+++ b/src/Application/Security/Ports/Services/RequestValidation/RequestValidationStatus.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Ports\Services\RequestValidation;
+
+enum RequestValidationStatus
+{
+    case VALID;
+    case CLIENT_NOT_AUTHORIZED;
+    case CLIENT_NOT_FOUND;
+    case INVALID_TIMESTAMP;
+    case INVALID_NONCE;
+    case INVALID_SIGNATURE;
+}
diff --git a/src/Application/Security/Ports/Services/RequestValidator.php b/src/Application/Security/Ports/Services/RequestValidator.php
new file mode 100644
index 0000000..2e844f8
--- /dev/null
+++ b/src/Application/Security/Ports/Services/RequestValidator.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Ports\Services;
+
+use Application\Security\Models\ValueObjects\Request\Request;
+use Application\Security\Ports\Services\RequestValidation\RequestValidationResult;
+
+interface RequestValidator
+{
+    public function validate(Request $request): RequestValidationResult;
+}
diff --git a/src/Application/Security/Ports/Services/TimestampValidator.php b/src/Application/Security/Ports/Services/TimestampValidator.php
new file mode 100644
index 0000000..8359fea
--- /dev/null
+++ b/src/Application/Security/Ports/Services/TimestampValidator.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Ports\Services;
+
+interface TimestampValidator
+{
+    public const int ALLOWED_TIMESTAMP_SKEW_SECONDS = 300; // 5 minutes
+
+    public function validate(\DateTimeInterface $timestamp): bool;
+}
diff --git a/src/Application/Security/Usecases/CreateClient/CreateClient.php b/src/Application/Security/Usecases/CreateClient/CreateClient.php
new file mode 100644
index 0000000..a115a3f
--- /dev/null
+++ b/src/Application/Security/Usecases/CreateClient/CreateClient.php
@@ -0,0 +1,59 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\CreateClient;
+
+use Application\Security\Events\ClientSecretGenerated;
+use Application\Security\Models\Entities\Client;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Application\Security\Ports\Repositories\ClientRepository;
+use Application\Security\Ports\Services\ClientCredentialGenerator;
+use Ramsey\Uuid\Uuid;
+use Shared\DDD\Event\DomainEventDispatcher;
+use Shared\DDD\Usecase\Input as BaseInput;
+use Shared\DDD\Usecase\Usecase;
+use Webmozart\Assert\Assert;
+
+/** @implements Usecase<\Application\Security\Usecases\CreateClient\Input, \Application\Security\Usecases\CreateClient\Output> */
+final readonly class CreateClient implements Usecase
+{
+    public function __construct(
+        private ClientRepository $clientRepository,
+        private ClientCredentialGenerator $credentialGenerator,
+        private DomainEventDispatcher $dispatcher,
+    ) {
+    }
+
+    #[\Override]
+    public function execute(BaseInput $input): Output
+    {
+        Assert::isInstanceOf($input, Input::class);
+
+        $clientId   = $input->clientId ?? new ClientId(Uuid::uuid7());
+        $identifier = $this->credentialGenerator->generateIdentifier();
+        $secret     = $this->credentialGenerator->generateSecret();
+
+        $client = Client::create(
+            id: $clientId,
+            name: $input->name,
+            identifier: $identifier,
+            secret: $secret,
+        );
+
+        $this->clientRepository->persist($client);
+
+        $this->dispatcher->dispatch(new ClientSecretGenerated(
+            $client->id,
+            $client->identifier,
+            new \DateTimeImmutable(),
+        ));
+
+        return new Output(
+            clientId: $client->id,
+            clientIdentifier: $client->identifier,
+            clientSecret: $client->secret,
+            clientName: $client->name,
+        );
+    }
+}
diff --git a/src/Application/Security/Usecases/CreateClient/Input.php b/src/Application/Security/Usecases/CreateClient/Input.php
new file mode 100644
index 0000000..b95e342
--- /dev/null
+++ b/src/Application/Security/Usecases/CreateClient/Input.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\CreateClient;
+
+use Application\Security\Models\ValueObjects\ClientName;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+
+final readonly class Input implements \Shared\DDD\Usecase\Input
+{
+    public function __construct(
+        public ClientName $name,
+        public ?ClientId $clientId = null,
+    ) {
+    }
+}
diff --git a/src/Application/Security/Usecases/CreateClient/Output.php b/src/Application/Security/Usecases/CreateClient/Output.php
new file mode 100644
index 0000000..01a21ec
--- /dev/null
+++ b/src/Application/Security/Usecases/CreateClient/Output.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\CreateClient;
+
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\ClientName;
+use Application\Security\Models\ValueObjects\ClientSecret;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+
+final readonly class Output implements \Shared\DDD\Usecase\Output
+{
+    public function __construct(
+        public ClientId $clientId,
+        public ClientIdentifier $clientIdentifier,
+        public ClientSecret $clientSecret,
+        public ClientName $clientName,
+    ) {
+    }
+}
diff --git a/src/Application/Security/Usecases/FindAllClients/FindAllClients.php b/src/Application/Security/Usecases/FindAllClients/FindAllClients.php
new file mode 100644
index 0000000..d72517c
--- /dev/null
+++ b/src/Application/Security/Usecases/FindAllClients/FindAllClients.php
@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\FindAllClients;
+
+use Application\Security\Models\Entities\Client;
+use Application\Security\Ports\Repositories\ClientRepository;
+use Shared\DDD\Usecase\Input as BaseInput;
+use Shared\DDD\Usecase\Usecase;
+use Shared\Paginated;
+use Webmozart\Assert\Assert;
+
+/** @implements Usecase<\Application\Security\Usecases\FindAllClients\Input, \Application\Security\Usecases\FindAllClients\Output> */
+final readonly class FindAllClients implements Usecase
+{
+    public function __construct(
+        private ClientRepository $repository,
+    ) {
+    }
+
+    #[\Override]
+    public function execute(BaseInput $input): Output
+    {
+        Assert::isInstanceOf($input, Input::class);
+
+        $page = $this->repository->findAll($input->pagination);
+
+        return $this->toOutput($page);
+    }
+
+    /**
+     * @param  Paginated<Client>  $resultPage
+     */
+    private function toOutput(Paginated $resultPage): Output
+    {
+        $pagination = $resultPage->getPagination();
+
+        return new Output(
+            clients: array_map(
+                static fn (Client $client): PaginatedClient => PaginatedClient::fromDomain($client),
+                $resultPage->getItems()
+            ),
+            total: $resultPage->getTotal(),
+            page: $pagination->pageNumber(),
+            perPage: $pagination->pageSize(),
+        );
+    }
+}
diff --git a/src/Application/Security/Usecases/FindAllClients/Input.php b/src/Application/Security/Usecases/FindAllClients/Input.php
new file mode 100644
index 0000000..53e8ec2
--- /dev/null
+++ b/src/Application/Security/Usecases/FindAllClients/Input.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\FindAllClients;
+
+use Shared\Pagination;
+
+final readonly class Input implements \Shared\DDD\Usecase\Input
+{
+    public function __construct(
+        public Pagination $pagination,
+    ) {
+    }
+}
diff --git a/src/Application/Security/Usecases/FindAllClients/Output.php b/src/Application/Security/Usecases/FindAllClients/Output.php
new file mode 100644
index 0000000..d0ac998
--- /dev/null
+++ b/src/Application/Security/Usecases/FindAllClients/Output.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\FindAllClients;
+
+use Shared\DDD\Usecase\Output as UsecaseOutput;
+
+final readonly class Output implements UsecaseOutput
+{
+    /**
+     * @param  array<PaginatedClient>  $clients
+     */
+    public function __construct(
+        public array $clients,
+        public int $total,
+        public int $page,
+        public int $perPage,
+    ) {
+    }
+}
diff --git a/src/Application/Security/Usecases/FindAllClients/PaginatedClient.php b/src/Application/Security/Usecases/FindAllClients/PaginatedClient.php
new file mode 100644
index 0000000..5ee173d
--- /dev/null
+++ b/src/Application/Security/Usecases/FindAllClients/PaginatedClient.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\FindAllClients;
+
+use Application\Security\Models\Entities\Client;
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\ClientName;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Shared\DDD\Usecase\Output as UsecaseOutput;
+
+final readonly class PaginatedClient implements UsecaseOutput
+{
+    public function __construct(
+        public ClientId $id,
+        public ClientIdentifier $identifier,
+        public ClientName $name,
+        public bool $isActive,
+        public \DateTimeInterface $createdAt,
+        public \DateTimeInterface $updatedAt,
+    ) {
+    }
+
+    public static function fromDomain(Client $client): self
+    {
+        return new self(
+            id: $client->id,
+            identifier: $client->identifier,
+            name: $client->name,
+            isActive: $client->isActive,
+            createdAt: $client->createdAt,
+            updatedAt: $client->updatedAt,
+        );
+    }
+}
diff --git a/src/Application/Security/Usecases/RegenerateClientSecret/Input.php b/src/Application/Security/Usecases/RegenerateClientSecret/Input.php
new file mode 100644
index 0000000..7421d21
--- /dev/null
+++ b/src/Application/Security/Usecases/RegenerateClientSecret/Input.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\RegenerateClientSecret;
+
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+
+final readonly class Input implements \Shared\DDD\Usecase\Input
+{
+    public function __construct(
+        public ClientId $clientId,
+    ) {
+    }
+}
diff --git a/src/Application/Security/Usecases/RegenerateClientSecret/Output.php b/src/Application/Security/Usecases/RegenerateClientSecret/Output.php
new file mode 100644
index 0000000..3fbfa73
--- /dev/null
+++ b/src/Application/Security/Usecases/RegenerateClientSecret/Output.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\RegenerateClientSecret;
+
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\ClientSecret;
+
+final readonly class Output implements \Shared\DDD\Usecase\Output
+{
+    public function __construct(
+        public ClientSecret $newSecret,
+        public ClientIdentifier $clientIdentifier,
+    ) {
+    }
+}
diff --git a/src/Application/Security/Usecases/RegenerateClientSecret/RegenerateClientSecret.php b/src/Application/Security/Usecases/RegenerateClientSecret/RegenerateClientSecret.php
new file mode 100644
index 0000000..a4c22a1
--- /dev/null
+++ b/src/Application/Security/Usecases/RegenerateClientSecret/RegenerateClientSecret.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\RegenerateClientSecret;
+
+use Application\Security\Events\ClientSecretRegenerated;
+use Application\Security\Exceptions\ClientNotFoundException;
+use Application\Security\Ports\Repositories\ClientRepository;
+use Application\Security\Ports\Services\ClientCredentialGenerator;
+use Shared\DDD\Event\DomainEventDispatcher;
+use Shared\DDD\Usecase\Input as BaseInput;
+use Shared\DDD\Usecase\Usecase;
+use Webmozart\Assert\Assert;
+
+/** @implements Usecase<\Application\Security\Usecases\RegenerateClientSecret\Input, \Application\Security\Usecases\RegenerateClientSecret\Output> */
+final readonly class RegenerateClientSecret implements Usecase
+{
+    public function __construct(
+        private ClientRepository $clientRepository,
+        private ClientCredentialGenerator $credentialGenerator,
+        private DomainEventDispatcher $dispatcher,
+    ) {
+    }
+
+    public function execute(BaseInput $input): Output
+    {
+        Assert::isInstanceOf($input, Input::class);
+
+        $client = $this->clientRepository->find($input->clientId) ?? throw new ClientNotFoundException();
+
+        $newSecret = $this->credentialGenerator->generateSecret();
+        $client->regenerateSecret($newSecret);
+        $this->clientRepository->persist($client);
+
+        $this->dispatcher->dispatch(new ClientSecretRegenerated(
+            $client->id,
+            $client->identifier,
+            new \DateTimeImmutable(),
+        ));
+
+        return new Output($newSecret, $client->identifier);
+    }
+}
diff --git a/src/Application/Security/Usecases/ToggleClientStatus/Input.php b/src/Application/Security/Usecases/ToggleClientStatus/Input.php
new file mode 100644
index 0000000..8bd5c1f
--- /dev/null
+++ b/src/Application/Security/Usecases/ToggleClientStatus/Input.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\ToggleClientStatus;
+
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+
+final readonly class Input implements \Shared\DDD\Usecase\Input
+{
+    public function __construct(
+        public ClientId $clientId,
+    ) {
+    }
+}
diff --git a/src/Application/Security/Usecases/ToggleClientStatus/Output.php b/src/Application/Security/Usecases/ToggleClientStatus/Output.php
new file mode 100644
index 0000000..89b3848
--- /dev/null
+++ b/src/Application/Security/Usecases/ToggleClientStatus/Output.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\ToggleClientStatus;
+
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\ClientName;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+
+final readonly class Output implements \Shared\DDD\Usecase\Output
+{
+    public function __construct(
+        public ClientId $clientId,
+        public ClientIdentifier $clientIdentifier,
+        public ClientName $clientName,
+        public bool $isActive,
+    ) {
+    }
+}
diff --git a/src/Application/Security/Usecases/ToggleClientStatus/ToggleClientStatus.php b/src/Application/Security/Usecases/ToggleClientStatus/ToggleClientStatus.php
new file mode 100644
index 0000000..458732d
--- /dev/null
+++ b/src/Application/Security/Usecases/ToggleClientStatus/ToggleClientStatus.php
@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Application\Security\Usecases\ToggleClientStatus;
+
+use Application\Security\Events\ClientStatusToggled;
+use Application\Security\Exceptions\ClientNotFoundException;
+use Application\Security\Ports\Repositories\ClientRepository;
+use Shared\DDD\Event\DomainEventDispatcher;
+use Shared\DDD\Usecase\Input as BaseInput;
+use Shared\DDD\Usecase\Usecase;
+use Webmozart\Assert\Assert;
+
+/** @implements Usecase<\Application\Security\Usecases\ToggleClientStatus\Input, \Application\Security\Usecases\ToggleClientStatus\Output> */
+final readonly class ToggleClientStatus implements Usecase
+{
+    public function __construct(
+        private ClientRepository $clientRepository,
+        private DomainEventDispatcher $dispatcher,
+    ) {
+    }
+
+    #[\Override]
+    public function execute(BaseInput $input): Output
+    {
+        Assert::isInstanceOf($input, Input::class);
+
+        $client = $this->clientRepository->find($input->clientId) ?? throw new ClientNotFoundException();
+
+        $isActive = $client->toggleStatus();
+        $this->clientRepository->persist($client);
+
+        $this->dispatcher->dispatch(new ClientStatusToggled(
+            clientId: $client->id,
+            clientIdentifier: $client->identifier,
+            isActive: $isActive,
+            toggledAt: new \DateTimeImmutable(),
+        ));
+
+        return new Output(
+            clientId: $client->id,
+            clientIdentifier: $client->identifier,
+            clientName: $client->name,
+            isActive: $isActive,
+        );
+    }
+}
diff --git a/tests/Unit/Application/Security/Usecases/CreateClient/CreateClientTest.php b/tests/Unit/Application/Security/Usecases/CreateClient/CreateClientTest.php
new file mode 100644
index 0000000..0f671db
--- /dev/null
+++ b/tests/Unit/Application/Security/Usecases/CreateClient/CreateClientTest.php
@@ -0,0 +1,120 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\Usecases\CreateClient;
+
+use Application\Security\Events\ClientSecretGenerated;
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\ClientName;
+use Application\Security\Models\ValueObjects\ClientSecret;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Application\Security\Ports\Services\ClientCredentialGenerator;
+use Application\Security\Usecases\CreateClient\CreateClient;
+use Application\Security\Usecases\CreateClient\Input;
+use Application\Security\Usecases\CreateClient\Output;
+use Infra\Adapters\Repositories\InMemoryClientRepository;
+use Mockery;
+use Ramsey\Uuid\Uuid;
+use Shared\DDD\Event\DomainEventDispatcher;
+
+covers(
+    CreateClient::class,
+    Input::class,
+    Output::class,
+);
+
+describe('CreateClient Usecase Unit Tests', function (): void {
+    $repository = new InMemoryClientRepository();
+
+    beforeEach(function () use ($repository): void {
+        $repository->clear();
+    });
+
+    it('creates and persists a new client with auto-generated id', function () use ($repository): void {
+        // GIVEN
+        $credentialGenerator = Mockery::mock(ClientCredentialGenerator::class);
+        $dispatcher          = Mockery::mock(DomainEventDispatcher::class);
+
+        $usecase = new CreateClient(
+            $repository,
+            $credentialGenerator,
+            $dispatcher
+        );
+
+        $name       = new ClientName('E-commerce Gateway');
+        $input      = new Input($name);
+        $identifier = new ClientIdentifier('arcadia_id_' . str_repeat('a', 32));
+        $secret     = new ClientSecret('arcadia_sec_' . str_repeat('b', 86));
+
+        $credentialGenerator->expects('generateIdentifier')
+            ->once()
+            ->andReturn($identifier);
+
+        $credentialGenerator->expects('generateSecret')
+            ->once()
+            ->andReturn($secret);
+
+        $dispatcher->expects('dispatch')
+            ->once()
+            ->withArgs(fn ($event): bool => $event instanceof ClientSecretGenerated
+                && $event->clientIdentifier->equals($identifier));
+
+        // WHEN
+        $result = $usecase->execute($input);
+
+        // THEN
+        expect($result)->toBeInstanceOf(Output::class)
+            ->and($result->clientName)->toBe($name)
+            ->and($result->clientIdentifier)->toBe($identifier)
+            ->and($result->clientSecret)->toBe($secret)
+            ->and($result->clientId)->toBeInstanceOf(ClientId::class);
+
+        $savedClient = $repository->find($result->clientId);
+        expect($savedClient)->not->toBeNull()
+            ->and($savedClient?->name)->toBe($name)
+            ->and($savedClient?->identifier)->toBe($identifier)
+            ->and($savedClient?->secret)->toBe($secret)
+            ->and($savedClient?->isActive)->toBeTrue();
+    });
+
+    it('creates and persists a new client with explicit client id', function () use ($repository): void {
+        // GIVEN
+        $credentialGenerator = Mockery::mock(ClientCredentialGenerator::class);
+        $dispatcher          = Mockery::mock(DomainEventDispatcher::class);
+
+        $usecase = new CreateClient(
+            $repository,
+            $credentialGenerator,
+            $dispatcher
+        );
+
+        $explicitId = new ClientId(Uuid::uuid7());
+        $name       = new ClientName('Mobile App Client');
+        $input      = new Input($name, $explicitId);
+        $identifier = new ClientIdentifier('arcadia_id_' . str_repeat('c', 32));
+        $secret     = new ClientSecret('arcadia_sec_' . str_repeat('d', 86));
+
+        $credentialGenerator->allows('generateIdentifier')
+            ->andReturn($identifier);
+
+        $credentialGenerator->allows('generateSecret')
+            ->andReturn($secret);
+
+        $dispatcher->allows('dispatch');
+
+        // WHEN
+        $result = $usecase->execute($input);
+
+        // THEN
+        expect($result)->toBeInstanceOf(Output::class)
+            ->and($result->clientId)->toBe($explicitId)
+            ->and($result->clientName)->toBe($name)
+            ->and($result->clientIdentifier)->toBe($identifier)
+            ->and($result->clientSecret)->toBe($secret);
+
+        $savedClient = $repository->find($explicitId);
+        expect($savedClient)->not->toBeNull()
+            ->and($savedClient?->id)->toBe($explicitId);
+    });
+});
diff --git a/tests/Unit/Application/Security/Usecases/FindAllClients/FindAllClientsTest.php b/tests/Unit/Application/Security/Usecases/FindAllClients/FindAllClientsTest.php
new file mode 100644
index 0000000..8808462
--- /dev/null
+++ b/tests/Unit/Application/Security/Usecases/FindAllClients/FindAllClientsTest.php
@@ -0,0 +1,85 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\Usecases\FindAllClients;
+
+use Application\Security\Models\Entities\Client;
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\ClientName;
+use Application\Security\Models\ValueObjects\ClientSecret;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Application\Security\Usecases\FindAllClients\FindAllClients;
+use Application\Security\Usecases\FindAllClients\Input;
+use Application\Security\Usecases\FindAllClients\Output;
+use Application\Security\Usecases\FindAllClients\PaginatedClient;
+use Infra\Adapters\Repositories\InMemoryClientRepository;
+use Ramsey\Uuid\Uuid;
+use Shared\Pagination;
+
+covers(
+    FindAllClients::class,
+    Input::class,
+    Output::class,
+    PaginatedClient::class,
+);
+
+describe('FindAllClients Usecase Unit Tests', function (): void {
+    $repository = new InMemoryClientRepository();
+
+    beforeEach(function () use ($repository): void {
+        $repository->clear();
+    });
+
+    function createTestClient(string $identifierSuffix, string $nameStr): Client
+    {
+        return Client::hydrate(
+            id: new ClientId(Uuid::uuid7()),
+            name: new ClientName($nameStr),
+            identifier: new ClientIdentifier('arcadia_id_' . str_repeat($identifierSuffix, 32)),
+            secret: new ClientSecret('arcadia_sec_' . str_repeat('a', 86)),
+            isActive: true,
+            createdAt: new \DateTimeImmutable('2024-01-01'),
+            updatedAt: new \DateTimeImmutable('2024-01-01'),
+        );
+    }
+
+    it('retrieves paginated clients list correctly', function () use ($repository): void {
+        // GIVEN
+        $client1 = createTestClient('1', 'Client Alpha');
+        $client2 = createTestClient('2', 'Client Beta');
+        $repository->add($client1, $client2);
+
+        $usecase    = new FindAllClients($repository);
+        $pagination = Pagination::ofPage(1, 10);
+        $input      = new Input($pagination);
+
+        // WHEN
+        $result = $usecase->execute($input);
+
+        // THEN
+        expect($result)->toBeInstanceOf(Output::class)
+            ->and($result->total)->toBe(2)
+            ->and($result->page)->toBe(1)
+            ->and($result->perPage)->toBe(10)
+            ->and($result->clients)->toHaveCount(2)
+            ->and($result->clients[0])->toBeInstanceOf(PaginatedClient::class)
+            ->and($result->clients[0]->name->value)->toBe('Client Alpha')
+            ->and($result->clients[1]->name->value)->toBe('Client Beta');
+    });
+
+    it('returns empty clients list when repository is empty', function () use ($repository): void {
+        // GIVEN
+        $usecase    = new FindAllClients($repository);
+        $pagination = Pagination::ofPage(1, 10);
+        $input      = new Input($pagination);
+
+        // WHEN
+        $result = $usecase->execute($input);
+
+        // THEN
+        expect($result)->toBeInstanceOf(Output::class)
+            ->and($result->total)->toBe(0)
+            ->and($result->clients)->toBeEmpty();
+    });
+});
diff --git a/tests/Unit/Application/Security/Usecases/RegenerateClientSecret/RegenerateClientSecretTest.php b/tests/Unit/Application/Security/Usecases/RegenerateClientSecret/RegenerateClientSecretTest.php
new file mode 100644
index 0000000..9fe511c
--- /dev/null
+++ b/tests/Unit/Application/Security/Usecases/RegenerateClientSecret/RegenerateClientSecretTest.php
@@ -0,0 +1,99 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\Usecases\RegenerateClientSecret;
+
+use Application\Security\Exceptions\ClientNotFoundException;
+use Application\Security\Models\Entities\Client;
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\ClientName;
+use Application\Security\Models\ValueObjects\ClientSecret;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Application\Security\Ports\Services\ClientCredentialGenerator;
+use Application\Security\Usecases\RegenerateClientSecret\Input;
+use Application\Security\Usecases\RegenerateClientSecret\Output;
+use Application\Security\Usecases\RegenerateClientSecret\RegenerateClientSecret;
+use Infra\Adapters\Repositories\InMemoryClientRepository;
+use Mockery;
+use Ramsey\Uuid\Uuid;
+use Shared\DDD\Event\DomainEventDispatcher;
+
+covers(
+    RegenerateClientSecret::class,
+    Input::class,
+    Output::class,
+);
+
+describe('RegenerateClientSecret Usecase Unit Tests', function (): void {
+    $repository = new InMemoryClientRepository();
+
+    beforeEach(function () use ($repository): void {
+        $repository->clear();
+    });
+
+    it('executes successfully and returns new credentials', function () use ($repository): void {
+        // GIVEN
+        $credentialGenerator = Mockery::mock(ClientCredentialGenerator::class);
+        $dispatcher          = Mockery::mock(DomainEventDispatcher::class);
+
+        $usecase = new RegenerateClientSecret(
+            $repository,
+            $credentialGenerator,
+            $dispatcher
+        );
+
+        $clientId          = new ClientId(Uuid::uuid7());
+        $input             = new Input($clientId);
+        $clientIdentifier  = new ClientIdentifier('arcadia_id_' . str_repeat('a', 32));
+        $oldSecret         = new ClientSecret('arcadia_sec_' . str_repeat('b', 86));
+        $newSecret         = new ClientSecret('arcadia_sec_' . str_repeat('c', 86));
+
+        $client = Client::hydrate(
+            id: $clientId,
+            name: new ClientName('Test Client'),
+            identifier: $clientIdentifier,
+            secret: $oldSecret,
+            isActive: true,
+            createdAt: new \DateTimeImmutable(),
+            updatedAt: new \DateTimeImmutable(),
+        );
+
+        $repository->add($client);
+
+        $credentialGenerator->allows('generateSecret')
+            ->andReturn($newSecret);
+
+        $dispatcher->allows('dispatch');
+
+        // WHEN
+        $result = $usecase->execute($input);
+
+        // THEN
+        expect($result)->toBeInstanceOf(Output::class)
+            ->and($result->newSecret)->toBe($newSecret)
+            ->and($result->clientIdentifier)->toBe($clientIdentifier)
+            ->and($repository->find($clientId)?->secret)->toBe($newSecret);
+    });
+
+    it('throws ClientNotFoundException when client does not exist', function () use ($repository): void {
+        // GIVEN
+        $credentialGenerator = Mockery::mock(ClientCredentialGenerator::class);
+        $dispatcher          = Mockery::mock(DomainEventDispatcher::class);
+
+        $usecase = new RegenerateClientSecret(
+            $repository,
+            $credentialGenerator,
+            $dispatcher
+        );
+
+        $clientId = new ClientId(Uuid::uuid7());
+        $input    = new Input($clientId);
+
+        // WHEN
+        $execution = fn () => $usecase->execute($input);
+
+        // THEN
+        expect($execution)->toThrow(ClientNotFoundException::class);
+    });
+});
diff --git a/tests/Unit/Application/Security/Usecases/ToggleClientStatus/ToggleClientStatusTest.php b/tests/Unit/Application/Security/Usecases/ToggleClientStatus/ToggleClientStatusTest.php
new file mode 100644
index 0000000..e8ff624
--- /dev/null
+++ b/tests/Unit/Application/Security/Usecases/ToggleClientStatus/ToggleClientStatusTest.php
@@ -0,0 +1,132 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\Usecases\ToggleClientStatus;
+
+use Application\Security\Events\ClientStatusToggled;
+use Application\Security\Exceptions\ClientNotFoundException;
+use Application\Security\Models\Entities\Client;
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+use Application\Security\Models\ValueObjects\ClientName;
+use Application\Security\Models\ValueObjects\ClientSecret;
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Application\Security\Usecases\ToggleClientStatus\Input;
+use Application\Security\Usecases\ToggleClientStatus\Output;
+use Application\Security\Usecases\ToggleClientStatus\ToggleClientStatus;
+use Infra\Adapters\Repositories\InMemoryClientRepository;
+use Mockery;
+use Ramsey\Uuid\Uuid;
+use Shared\DDD\Event\DomainEventDispatcher;
+
+covers(
+    ToggleClientStatus::class,
+    Input::class,
+    Output::class,
+);
+
+describe('ToggleClientStatus Usecase Unit Tests', function (): void {
+    $repository = new InMemoryClientRepository();
+
+    beforeEach(function () use ($repository): void {
+        $repository->clear();
+    });
+
+    it('toggles an active client to inactive and dispatches event', function () use ($repository): void {
+        // GIVEN
+        $dispatcher = Mockery::mock(DomainEventDispatcher::class);
+        $usecase    = new ToggleClientStatus($repository, $dispatcher);
+
+        $clientId   = new ClientId(Uuid::uuid7());
+        $identifier = new ClientIdentifier('arcadia_id_' . str_repeat('a', 32));
+        $name       = new ClientName('Test Gateway');
+        $secret     = new ClientSecret('arcadia_sec_' . str_repeat('b', 86));
+
+        $client = Client::hydrate(
+            id: $clientId,
+            name: $name,
+            identifier: $identifier,
+            secret: $secret,
+            isActive: true,
+            createdAt: new \DateTimeImmutable(),
+            updatedAt: new \DateTimeImmutable(),
+        );
+
+        $repository->add($client);
+
+        $dispatcher->expects('dispatch')
+            ->once()
+            ->withArgs(fn ($event): bool => $event instanceof ClientStatusToggled
+                && $event->clientId->equals($clientId)
+                && $event->isActive === false);
+
+        $input = new Input($clientId);
+
+        // WHEN
+        $result = $usecase->execute($input);
+
+        // THEN
+        expect($result)->toBeInstanceOf(Output::class)
+            ->and($result->clientId)->toBe($clientId)
+            ->and($result->clientIdentifier)->toBe($identifier)
+            ->and($result->clientName)->toBe($name)
+            ->and($result->isActive)->toBeFalse();
+
+        $saved = $repository->find($clientId);
+        expect($saved?->isActive)->toBeFalse();
+    });
+
+    it('toggles an inactive client to active and dispatches event', function () use ($repository): void {
+        // GIVEN
+        $dispatcher = Mockery::mock(DomainEventDispatcher::class);
+        $usecase    = new ToggleClientStatus($repository, $dispatcher);
+
+        $clientId   = new ClientId(Uuid::uuid7());
+        $identifier = new ClientIdentifier('arcadia_id_' . str_repeat('a', 32));
+        $name       = new ClientName('Inactive Client');
+        $secret     = new ClientSecret('arcadia_sec_' . str_repeat('b', 86));
+
+        $client = Client::hydrate(
+            id: $clientId,
+            name: $name,
+            identifier: $identifier,
+            secret: $secret,
+            isActive: false,
+            createdAt: new \DateTimeImmutable(),
+            updatedAt: new \DateTimeImmutable(),
+        );
+
+        $repository->add($client);
+
+        $dispatcher->expects('dispatch')
+            ->once()
+            ->withArgs(fn ($event): bool => $event instanceof ClientStatusToggled
+                && $event->clientId->equals($clientId)
+                && $event->isActive === true);
+
+        $input = new Input($clientId);
+
+        // WHEN
+        $result = $usecase->execute($input);
+
+        // THEN
+        expect($result)->toBeInstanceOf(Output::class)
+            ->and($result->isActive)->toBeTrue();
+
+        $saved = $repository->find($clientId);
+        expect($saved?->isActive)->toBeTrue();
+    });
+
+    it('throws ClientNotFoundException when client does not exist', function () use ($repository): void {
+        // GIVEN
+        $dispatcher = Mockery::mock(DomainEventDispatcher::class);
+        $usecase    = new ToggleClientStatus($repository, $dispatcher);
+
+        $clientId = new ClientId(Uuid::uuid7());
+        $input    = new Input($clientId);
+
+        // WHEN & THEN
+        expect(fn () => $usecase->execute($input))
+            ->toThrow(ClientNotFoundException::class);
+    });
+});
diff --git a/tests/Unit/Application/Security/ValueObjects/ClientIdentifierTest.php b/tests/Unit/Application/Security/ValueObjects/ClientIdentifierTest.php
new file mode 100644
index 0000000..1a7095a
--- /dev/null
+++ b/tests/Unit/Application/Security/ValueObjects/ClientIdentifierTest.php
@@ -0,0 +1,93 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\ValueObjects;
+
+use Application\Security\Models\ValueObjects\ClientIdentifier;
+
+covers(ClientIdentifier::class);
+
+describe('ClientIdentifier Value Object Instantiation', function (): void {
+    it('instantiates successfully with a valid client identifier', function (string $input): void {
+        // GIVEN
+        $validClientIdentifier = $input;
+
+        // WHEN
+        $clientIdentifier = new ClientIdentifier($validClientIdentifier);
+
+        // THEN
+        expect($clientIdentifier->value)->toBe($validClientIdentifier)
+            ->and($clientIdentifier->value())->toBe($validClientIdentifier);
+    })->with([
+        'arcadia_id_' . str_repeat('a', 32),
+        str_repeat('c', 43),
+        str_repeat('x', 255),
+        'client-identifier_with-valid_chars-1234567890123456',
+    ]);
+});
+
+describe('ClientIdentifier Value Object Validation Rules', function (): void {
+    it('throws InvalidArgumentException when given an empty client identifier', function (string $invalid): void {
+        // GIVEN
+        $input = $invalid;
+
+        // WHEN
+        $execution = fn () => new ClientIdentifier($input);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'ClientIdentifier cannot be empty.'
+        );
+    })->with(['', '   ']);
+
+    it('throws InvalidArgumentException when client identifier format contains invalid characters', function (string $invalid): void {
+        // GIVEN
+        $input = $invalid;
+
+        // WHEN
+        $execution = fn () => new ClientIdentifier($input);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'ClientIdentifier can only contain alphanumeric characters, dashes, and underscores.'
+        );
+    })->with([
+        'arcadia_id_with_invalid_char_@_' . str_repeat('a', 20),
+        'arcadia_id with spaces in between' . str_repeat('a', 20),
+        'arcadia_id!@#$%^&*()_+' . str_repeat('a', 30),
+    ]);
+
+    it('throws InvalidArgumentException when client identifier is too short', function (string $invalid): void {
+        // GIVEN
+        $input = $invalid;
+
+        // WHEN
+        $execution = fn () => new ClientIdentifier($input);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'ClientIdentifier must be at least 43 characters long.'
+        );
+    })->with([
+        str_repeat('a', 42),
+        'arcadia_id_short',
+    ]);
+
+    it('throws InvalidArgumentException when client identifier exceeds 255 characters', function (): void {
+        // GIVEN
+        $input = str_repeat('a', 256);
+
+        // WHEN
+        $execution = fn () => new ClientIdentifier($input);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'ClientIdentifier cannot exceed 255 characters.'
+        );
+    });
+});
diff --git a/tests/Unit/Application/Security/ValueObjects/ClientNameTest.php b/tests/Unit/Application/Security/ValueObjects/ClientNameTest.php
new file mode 100644
index 0000000..67fdd64
--- /dev/null
+++ b/tests/Unit/Application/Security/ValueObjects/ClientNameTest.php
@@ -0,0 +1,56 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\ValueObjects;
+
+use Application\Security\Models\ValueObjects\ClientName;
+
+covers(ClientName::class);
+
+describe('ClientName Value Object Instantiation', function (): void {
+    it('accepts valid client names', function (string $input): void {
+        // GIVEN
+        $value = $input;
+
+        // WHEN
+        $clientName = new ClientName($value);
+
+        // THEN
+        expect($clientName->value)->toBe($value);
+    })->with([
+        'Arcadia Test Client',
+        'A',
+        str_repeat('b', 255),
+    ]);
+});
+
+describe('ClientName Value Object Validation Rules', function (): void {
+    it('throws InvalidArgumentException when given an empty client name', function (): void {
+        // GIVEN
+        $invalid = '';
+
+        // WHEN
+        $execution = fn () => new ClientName($invalid);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'ClientName cannot be empty.'
+        );
+    });
+
+    it('throws InvalidArgumentException when client name exceeds 255 characters', function (): void {
+        // GIVEN
+        $invalid = str_repeat('a', 256);
+
+        // WHEN
+        $execution = fn () => new ClientName($invalid);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'ClientName cannot exceed 255 characters.'
+        );
+    });
+});
diff --git a/tests/Unit/Application/Security/ValueObjects/ClientSecretTest.php b/tests/Unit/Application/Security/ValueObjects/ClientSecretTest.php
new file mode 100644
index 0000000..123fcab
--- /dev/null
+++ b/tests/Unit/Application/Security/ValueObjects/ClientSecretTest.php
@@ -0,0 +1,77 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\ValueObjects;
+
+use Application\Security\Models\ValueObjects\ClientSecret;
+
+covers(ClientSecret::class);
+
+describe('ClientSecret Value Object Instantiation', function (): void {
+    it('accepts valid client secrets', function (string $input): void {
+        // GIVEN
+        $value = $input;
+
+        // WHEN
+        $clientSecret = new ClientSecret($value);
+
+        // THEN
+        expect($clientSecret->value)->toBe($value);
+    })->with([
+        'arcadia_sec_' . str_repeat('b', 86),
+        str_repeat('s', 86),
+        str_repeat('s', 98),
+        str_repeat('s', 120),
+    ]);
+});
+
+describe('ClientSecret Value Object Validation Rules', function (): void {
+    it('throws InvalidArgumentException when given an empty or whitespace-only client secret', function (string $invalid): void {
+        // GIVEN
+        $input = $invalid;
+
+        // WHEN
+        $execution = fn () => new ClientSecret($input);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'ClientSecret cannot be empty.'
+        );
+    })->with(['', '   ']);
+
+    it('throws InvalidArgumentException when client secret contains invalid characters', function (string $invalid): void {
+        // GIVEN
+        $input = $invalid;
+
+        // WHEN
+        $execution = fn () => new ClientSecret($input);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'ClientSecret can only contain alphanumeric characters, dashes, and underscores.'
+        );
+    })->with([
+        'arcadia_sec_invalid_chars_@!' . str_repeat('a', 60),
+        'arcadia_sec with spaces in between' . str_repeat('a', 60),
+    ]);
+
+    it('throws InvalidArgumentException when client secret has an invalid length', function (string $invalid): void {
+        // GIVEN
+        $input = $invalid;
+
+        // WHEN
+        $execution = fn () => new ClientSecret($input);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'ClientSecret must be between 86 and 120 characters long.'
+        );
+    })->with([
+        str_repeat('a', 85),
+        str_repeat('a', 121),
+    ]);
+});
diff --git a/tests/Unit/Application/Security/ValueObjects/Entities/ClientIdTest.php b/tests/Unit/Application/Security/ValueObjects/Entities/ClientIdTest.php
new file mode 100644
index 0000000..4e01c89
--- /dev/null
+++ b/tests/Unit/Application/Security/ValueObjects/Entities/ClientIdTest.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\ValueObjects\Entities;
+
+use Application\Security\Models\ValueObjects\Entities\ClientId;
+use Ramsey\Uuid\Uuid;
+use Ramsey\Uuid\UuidInterface;
+use Shared\Helpers\Exceptions\InvalidUuidException;
+
+covers(ClientId::class);
+
+describe('ClientId Value Object Instantiation', function (): void {
+    it('accepts valid UUIDv7 identifier', function (): void {
+        // GIVEN
+        $uuid7 = Uuid::uuid7();
+
+        // WHEN
+        $clientId = new ClientId($uuid7);
+
+        // THEN
+        expect($clientId->identifier)->toBe($uuid7)
+            ->and($clientId->value)->toBe($uuid7->toString());
+    });
+});
+
+describe('ClientId Value Object Validation Rules', function (): void {
+    it('throws InvalidUuidException when given a non-v7 UUID identifier', function (UuidInterface $nonV7Uuid): void {
+        // GIVEN
+        $input = $nonV7Uuid;
+
+        // WHEN
+        $execution = fn () => new ClientId($input);
+
+        // THEN
+        expect($execution)->toThrow(InvalidUuidException::class);
+    })->with([
+        fn () => Uuid::uuid4(),
+        fn () => Uuid::uuid1(),
+    ]);
+});
diff --git a/tests/Unit/Application/Security/ValueObjects/Request/HttpBodyHashTest.php b/tests/Unit/Application/Security/ValueObjects/Request/HttpBodyHashTest.php
new file mode 100644
index 0000000..343f008
--- /dev/null
+++ b/tests/Unit/Application/Security/ValueObjects/Request/HttpBodyHashTest.php
@@ -0,0 +1,63 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\ValueObjects\Request;
+
+use Application\Security\Models\ValueObjects\Request\HttpBodyHash;
+
+covers(HttpBodyHash::class);
+
+describe('HttpBodyHash Value Object Instantiation', function (): void {
+    it('accepts valid SHA256 hex hashes', function (string $input): void {
+        // GIVEN
+        $value = $input;
+
+        // WHEN
+        $bodyHash = new HttpBodyHash($value);
+
+        // THEN
+        expect($bodyHash->value)->toBe($value);
+    })->with([
+        hash('sha256', ''),
+        hash('sha256', 'payload content'),
+        str_repeat('a', 64),
+        str_repeat('F', 64),
+    ]);
+});
+
+describe('HttpBodyHash Value Object Validation Rules', function (): void {
+    it('throws InvalidArgumentException when given an empty body hash', function (): void {
+        // GIVEN
+        $invalid = '';
+
+        // WHEN
+        $execution = fn () => new HttpBodyHash($invalid);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'HttpBody cannot be empty'
+        );
+    });
+
+    it('throws InvalidArgumentException when given an invalid SHA256 hash', function (string $invalid): void {
+        // GIVEN
+        $input = $invalid;
+
+        // WHEN
+        $execution = fn () => new HttpBodyHash($input);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'HttpBody must be a valid SHA256 hash'
+        );
+    })->with([
+        'invalid_hash',
+        '12345',
+        str_repeat('g', 64), // Invalid hex character
+        str_repeat('a', 63), // 63 chars (too short)
+        str_repeat('a', 65), // 65 chars (too long)
+    ]);
+});
diff --git a/tests/Unit/Application/Security/ValueObjects/Request/NonceTest.php b/tests/Unit/Application/Security/ValueObjects/Request/NonceTest.php
new file mode 100644
index 0000000..e21586a
--- /dev/null
+++ b/tests/Unit/Application/Security/ValueObjects/Request/NonceTest.php
@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\ValueObjects\Request;
+
+use Application\Security\Models\ValueObjects\Request\Nonce;
+use Ramsey\Uuid\Uuid;
+
+covers(Nonce::class);
+
+describe('Nonce Value Object Instantiation', function (): void {
+    it('accepts valid UUID instance', function (): void {
+        // GIVEN
+        $uuid = Uuid::uuid7();
+
+        // WHEN
+        $nonce = new Nonce($uuid);
+
+        // THEN
+        expect($nonce->value)->toBe($uuid);
+    });
+});
diff --git a/tests/Unit/Application/Security/ValueObjects/Request/RequestSignatureTest.php b/tests/Unit/Application/Security/ValueObjects/Request/RequestSignatureTest.php
new file mode 100644
index 0000000..9d3515e
--- /dev/null
+++ b/tests/Unit/Application/Security/ValueObjects/Request/RequestSignatureTest.php
@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\ValueObjects\Request;
+
+use Application\Security\Models\ValueObjects\Request\RequestSignature;
+
+covers(RequestSignature::class);
+
+describe('RequestSignature Value Object Instantiation', function (): void {
+    it('instantiates successfully with a valid 64-character hex signature', function (): void {
+        // GIVEN
+        $validSignature = hash_hmac('sha256', 'test_payload', 'secret_key');
+
+        // WHEN
+        $signature = new RequestSignature($validSignature);
+
+        // THEN
+        expect($signature->value)->toBe($validSignature);
+    });
+});
+
+describe('RequestSignature Value Object Validation Rules', function (): void {
+    it('throws InvalidArgumentException when given an empty signature', function (string $invalid): void {
+        // GIVEN
+        $input = $invalid;
+
+        // WHEN
+        $execution = fn () => new RequestSignature($input);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'RequestSignature cannot be empty.'
+        );
+    })->with(['', '   ']);
+
+    it('throws InvalidArgumentException when signature format is invalid', function (string $invalid): void {
+        // GIVEN
+        $input = $invalid;
+
+        // WHEN
+        $execution = fn () => new RequestSignature($input);
+
+        // THEN
+        expect($execution)->toThrow(
+            \InvalidArgumentException::class,
+            'RequestSignature must be a valid 64-character hex HMAC-SHA256 string.'
+        );
+    })->with([
+        'invalid_hex',
+        '123456',
+        str_repeat('g', 64), // Invalid hex character 'g'
+        str_repeat('a', 63), // 63 chars (too short)
+        str_repeat('a', 65), // 65 chars (too long)
+    ]);
+});
diff --git a/tests/Unit/Application/Security/ValueObjects/Request/RequestTimestampTest.php b/tests/Unit/Application/Security/ValueObjects/Request/RequestTimestampTest.php
new file mode 100644
index 0000000..9172346
--- /dev/null
+++ b/tests/Unit/Application/Security/ValueObjects/Request/RequestTimestampTest.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Application\Security\ValueObjects\Request;
+
+use Application\Security\Models\ValueObjects\Request\RequestTimestamp;
+
+covers(RequestTimestamp::class);
+
+describe('RequestTimestamp Value Object Instantiation', function (): void {
+    it('accepts valid DateTimeImmutable instance', function (): void {
+        // GIVEN
+        $dateTime = new \DateTimeImmutable('2026-08-18 10:00:00');
+
+        // WHEN
+        $timestamp = new RequestTimestamp($dateTime);
+
+        // THEN
+        expect($timestamp->value)->toBe($dateTime);
+    });
+});