Restore custom JWT principal

src/main/kotlin/me/wypark/blogbackend/core/config/jwt/JwtProvider.kt

@@ -10,7 +10,6 @@ import org.springframework.security.authentication.UsernamePasswordAuthenticatio
 import org.springframework.security.core.Authentication
 import org.springframework.security.core.GrantedAuthority
 import org.springframework.security.core.authority.SimpleGrantedAuthority
-import org.springframework.security.core.userdetails.User
 import org.springframework.stereotype.Component
 import java.util.*
 import javax.crypto.SecretKey
@@ -90,7 +89,19 @@ class JwtProvider(
                 .map { SimpleGrantedAuthority(it) }
 
         // UserDetails 객체를 생성하여 Authentication에 담음 (비밀번호는 불필요하므로 빈 문자열)
-        val principal = User(claims.subject, "", authorities)
+        val memberId = when (val claim = claims["memberId"]) {
+            is Number -> claim.toLong()
+            is String -> claim.toLong()
+            else -> throw RuntimeException("memberId claim is missing.")
+        }
+        val nickname = claims["nickname"]?.toString() ?: claims.subject
+        val principal = CustomUserDetails(
+            memberId = memberId,
+            nickname = nickname,
+            username = claims.subject,
+            password = "",
+            authorities = authorities
+        )
         return UsernamePasswordAuthenticationToken(principal, "", authorities)
     }
 
@@ -126,4 +137,4 @@ class JwtProvider(
             e.claims
         }
     }
-}
+}

src/test/kotlin/me/wypark/blogbackend/core/config/jwt/JwtProviderTest.kt

@@ -0,0 +1,43 @@
+package me.wypark.blogbackend.core.config.jwt
+
+import me.wypark.blogbackend.domain.auth.CustomUserDetails
+import org.junit.jupiter.api.Test
+import org.springframework.security.authentication.UsernamePasswordAuthenticationToken
+import org.springframework.security.core.authority.SimpleGrantedAuthority
+import kotlin.test.assertEquals
+import kotlin.test.assertIs
+
+class JwtProviderTest {
+
+    private val jwtProvider = JwtProvider(
+        secretKey = "c2VjcmV0LWtleS1mb3ItdGVzdC1hZG1pbi1kYXNoYm9hcmQtMzItYnl0ZXM=",
+        accessTokenValidity = 600000,
+        refreshTokenValidity = 604800000
+    )
+
+    @Test
+    fun `access token authentication restores custom user details`() {
+        val originalPrincipal = CustomUserDetails(
+            memberId = 2L,
+            nickname = "tester",
+            username = "tester@example.com",
+            password = "",
+            authorities = listOf(SimpleGrantedAuthority("ROLE_ADMIN"))
+        )
+        val token = jwtProvider.generateTokenDto(
+            UsernamePasswordAuthenticationToken(
+                originalPrincipal,
+                "",
+                originalPrincipal.authorities
+            )
+        )
+
+        val authentication = jwtProvider.getAuthentication(token.accessToken)
+        val principal = assertIs<CustomUserDetails>(authentication.principal)
+
+        assertEquals(2L, principal.memberId)
+        assertEquals("tester", principal.nickname)
+        assertEquals("tester@example.com", principal.username)
+        assertEquals("ROLE_ADMIN", authentication.authorities.single().authority)
+    }
+}