[BOOK-52] refactor: apis - Exception 추가 (#11)

Author: minwoo1999

apis/src/main/kotlin/org/yapp/apis/auth/exception/AuthErrorCode.kt

@@ -22,7 +22,8 @@ enum class AuthErrorCode(
     INVALID_ID_TOKEN_FORMAT(HttpStatus.BAD_REQUEST, "AUTH_008", "Invalid ID token format."),
     SUBJECT_NOT_FOUND(HttpStatus.BAD_REQUEST, "AUTH_009", "Subject not found in ID token."),
     FAILED_TO_PARSE_ID_TOKEN(HttpStatus.BAD_REQUEST, "AUTH_010", "Failed to parse ID token."),
-    FAILED_TO_GET_USER_INFO(HttpStatus.BAD_REQUEST, "AUTH_011", "Failed to get user info from provider.");
+    FAILED_TO_GET_USER_INFO(HttpStatus.BAD_REQUEST, "AUTH_011", "Failed to get user info from provider."),
+    USER_NOT_FOUND(HttpStatus.BAD_REQUEST, "AUTH_012", "User not found.");
 
     override fun getHttpStatus(): HttpStatus = httpStatus
     override fun getCode(): String = code

apis/src/main/kotlin/org/yapp/apis/auth/service/AuthServiceImpl.kt

@@ -1,6 +1,7 @@
 package org.yapp.apis.auth.service
 
 import org.springframework.stereotype.Service
+import org.yapp.apis.auth.dto.TokenPair
 import org.yapp.apis.auth.dto.UserProfileResponse
 import org.yapp.apis.auth.exception.AuthErrorCode
 import org.yapp.apis.auth.exception.AuthException
@@ -32,7 +33,9 @@ class AuthServiceImpl(
         )
 
         if (existingUser != null) {
-            return generateTokenPair(existingUser.id!!)
+            return generateTokenPair(
+                existingUser.id ?: throw IllegalStateException("Existing user id should not be null")
+            )
         }
 
         userRepository.findByEmail(userInfo.email)?.let {
@@ -70,11 +73,10 @@ class AuthServiceImpl(
         tokenRepository.deleteRefreshToken(userId)
     }
 
-    override fun getUserById(userId: Long): User? = null
+    override fun getUserById(userId: Long): User? = userRepository.findById(userId)
 
     override fun getUserProfile(userId: Long): UserProfileResponse {
         val user = userRepository.findById(userId)
-
         return UserProfileResponse(
             id = user.id!!,
             email = user.email,
@@ -98,7 +100,10 @@ class AuthServiceImpl(
 
     private fun getAuthStrategy(credentials: AuthCredentials): AuthStrategy {
         return authStrategies.find { it.getProviderType() == credentials.getProviderType() }
-            ?: throw AuthException(AuthErrorCode.UNSUPPORTED_PROVIDER_TYPE, "Unsupported provider type: ${credentials.getProviderType()}")
+            ?: throw AuthException(
+                AuthErrorCode.UNSUPPORTED_PROVIDER_TYPE,
+                "Unsupported provider type: ${credentials.getProviderType()}"
+            )
     }
 
     private fun generateTokenPair(userId: Long): TokenPair {