feat: create user application service

src/main/kotlin/application/service/UserService.kt

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2023. Smart Operating Block
+ *
+ * Use of this source code is governed by an MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT.
+ */
+
+package application.service
+
+import entity.user.User
+import usecase.repository.UserRepository
+
+/**
+ * The application service for user management.
+ * @param userRepository the repository to access user data.
+ */
+class UserService(private val userRepository: UserRepository) {
+
+    /** Get a user given its [userId]. */
+    fun getUser(userId: String): User? = userRepository.getUser(userId)
+
+    /** Create a [User]. */
+    fun createUser(user: User): User? = userRepository.createUser(user)
+
+    /** Delete a [User] given its [userId]. */
+    fun deleteUser(userId: String): Boolean = userRepository.deleteUser(userId)
+}

src/main/kotlin/usecase/AuthenticationUseCase.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2023. Smart Operating Block
+ *
+ * Use of this source code is governed by an MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT.
+ */
+
+package usecase
+
+import usecase.repository.UserRepository
+
+/**
+ * The use case of user authentication given the [userId] and the [password].
+ * @param userRepository the repository to access user data.
+ */
+class AuthenticationUseCase(
+    private val userId: String,
+    private val password: String,
+    private val userRepository: UserRepository
+) : UseCase<Boolean> {
+
+    override fun execute(): Boolean =
+        userRepository.getUser(userId).let {
+            it?.password.equals(password)
+        }
+}