Add JWT 토큰 인증 방식으로 변경, JWT 커스텀 필터 추가

src/main/java/com/example/springsecuritystudy/jwt/SigningKeyResolver.java

@@ -0,0 +1,22 @@
+package com.example.springsecuritystudy.jwt;
+
+import java.security.Key;
+
+import io.jsonwebtoken.Claims;
+import io.jsonwebtoken.JwsHeader;
+import io.jsonwebtoken.SigningKeyResolverAdapter;
+
+/**
+ * JwsHeader를 통해 Signature 검증에 필요한 Key를 가져오는 코드를 구현합니다.
+ */
+public class SigningKeyResolver extends SigningKeyResolverAdapter {
+	public static SigningKeyResolver instance = new SigningKeyResolver();
+
+	@Override
+	public Key resolveSigningKey(JwsHeader jwsHeader, Claims claims) {
+		String kid = jwsHeader.getKeyId();
+		if (kid == null)
+			return null;
+		return JwtKey.getKey(kid);
+	}
+}