add PrivateJwtService

src/main/kotlin/ltd/hlaeja/jwt/service/PrivateJwtService.kt

@@ -0,0 +1,26 @@
+package ltd.hlaeja.jwt.service
+
+import io.jsonwebtoken.Jwts
+import java.security.interfaces.RSAPrivateKey
+import ltd.hlaeja.jwt.util.PrivateKeyProvider
+import org.springframework.beans.factory.annotation.Value
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty
+import org.springframework.stereotype.Service
+
+@Service
+@ConditionalOnProperty(prefix = "jwt", name = ["private-key"])
+class PrivateJwtService(
+    @Value("\${jwt.private-key}") jwtPrivateKey: String,
+) {
+
+    private var privateKey: RSAPrivateKey = PrivateKeyProvider.load(jwtPrivateKey)
+
+    fun sign(
+        vararg claim: Pair<String, Any>,
+    ): String = Jwts.builder()
+        .claims()
+        .also { claims -> claim.forEach { claims.add(it.first, it.second) } }
+        .and()
+        .signWith(privateKey)
+        .compact()
+}