Add JWTAuthorizer Implementation.

java/app/build.gradle

@@ -59,6 +59,8 @@ dependencies {
   implementation('org.glassfish.jersey.inject:jersey-hk2:3.1.0')
   implementation "org.glassfish.hk2:guice-bridge:3.0.3"
 
+  implementation "com.auth0:java-jwt:4.2.0"
+
   compileOnly 'org.projectlombok:lombok:1.18.24'
   annotationProcessor 'org.projectlombok:lombok:1.18.24'
 

java/app/src/main/java/org/vss/auth/JwtAuthorizer.java

@@ -0,0 +1,80 @@
+package org.vss.auth;
+
+import com.auth0.jwt.JWT;
+import com.auth0.jwt.algorithms.Algorithm;
+import com.auth0.jwt.exceptions.JWTVerificationException;
+import com.auth0.jwt.interfaces.DecodedJWT;
+import com.auth0.jwt.interfaces.JWTVerifier;
+import jakarta.ws.rs.core.HttpHeaders;
+import org.vss.exception.AuthException;
+
+import java.security.KeyFactory;
+import java.security.PublicKey;
+import java.security.interfaces.RSAPublicKey;
+import java.security.spec.X509EncodedKeySpec;
+import java.util.Base64;
+
+// A JWT (https://datatracker.ietf.org/doc/html/rfc7519) based authorizer,
+public class JwtAuthorizer implements Authorizer {
+
+	private final PublicKey publicKey;
+	private final JWTVerifier verifier;
+
+	private static final String BEARER_PREFIX = "Bearer ";
+	private static final int MAX_USER_TOKEN_LENGTH = 120;
+
+	// `pemFormatRSAPublicKey` is RSA public key used by JWT Auth server for creating signed JWT tokens.
+	// Refer to OpenSSL(https://docs.openssl.org/1.1.1/man1/rsa/) docs for generating valid key pairs.
+	// Example:
+	// * To generate private key, run : `openssl genpkey -algorithm RSA -out private_key.pem -pkeyopt rsa_keygen_bits:2048`
+	// * To generate public key, run: `openssl rsa -pubout -in private_key.pem -out public_key.pem`
+	public JwtAuthorizer(String pemFormatRSAPublicKey) throws Exception {
+		this.publicKey = loadPublicKey(pemFormatRSAPublicKey);
+
+		Algorithm algorithm = Algorithm.RSA256((RSAPublicKey) publicKey, null);
+		this.verifier = JWT.require(algorithm).build();
+	}
+
+	@Override
+	public AuthResponse verify(HttpHeaders headers) throws AuthException {
+
+		try {
+			String authorizationHeader = headers.getHeaderString(HttpHeaders.AUTHORIZATION);
+			if (authorizationHeader == null || !authorizationHeader.startsWith(BEARER_PREFIX)) {
+				throw new AuthException("Missing or invalid Authorization header.");
+			}
+
+			// Extract token by excluding BEARER_PREFIX.
+			String token = authorizationHeader.substring(BEARER_PREFIX.length());
+
+			DecodedJWT jwt = verifier.verify(token);
+
+			// Extract the user identity from the token.
+			String userToken = jwt.getSubject();
+
+			if (userToken == null || userToken.isBlank()) {
+				throw new AuthException("Invalid JWT token.");
+			} else if (userToken.length() > MAX_USER_TOKEN_LENGTH) {
+				throw new AuthException("UserToken is too long");
+			}
+
+			return new AuthResponse(userToken);
+
+		} catch (JWTVerificationException e) {
+			throw new AuthException("Invalid JWT token.");
+		}
+	}
+
+	private PublicKey loadPublicKey(String pemFormatRSAPublicKey) throws Exception {
+		String key = pemFormatRSAPublicKey
+				.replaceAll("\\n", "")
+				.replace("-----BEGIN PUBLIC KEY-----", "")
+				.replace("-----END PUBLIC KEY-----", "");
+
+		byte[] keyBytes = Base64.getDecoder().decode(key);
+
+		X509EncodedKeySpec spec = new X509EncodedKeySpec(keyBytes);
+		KeyFactory keyFactory = KeyFactory.getInstance("RSA");
+		return keyFactory.generatePublic(spec);
+	}
+}

java/app/src/test/java/org/vss/auth/JwtAuthorizerTest.java

@@ -0,0 +1,75 @@
+package org.vss.auth;
+
+import jakarta.ws.rs.core.HttpHeaders;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.vss.exception.AuthException;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+class JwtAuthorizerTest {
+
+	private JwtAuthorizer jwtAuthorizer;
+	private HttpHeaders headers;
+
+	private static final String PUBLIC_KEY = "-----BEGIN PUBLIC KEY-----\n" +
+			"MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAysGpKU+I9i9b+QZSANu/\n" +
+			"ExaA6w4qiQdFZaXeReiz49r1oDfABwKIFW9gK/kNnrnL9H8P+pYfj7jqUJ/glmgq\n" +
+			"MsvBshbbD2FhxytSS0mhsbh6QxUhlanymPcSUUyKBD6v7W0CGUhS5luHlsCFn4ys\n" +
+			"lFk4pavcBtGap0DTUc8yz0j/xnmSQbdjWgm0awbHN48uItRO3UhLAOetG+BzlWCR\n" +
+			"8YsTa5piV8KgJpG/rwYTGXuu3lcCmnWwjmbeDq1zFFrCDDVkaIHkGJgRuFIDPXaH\n" +
+			"yUw5H2HvKlP94ySbvTDLXWZj6TyzHEHDbstqs4DgvurB/bIhi/dQ7zK3EIXL8KRB\n" +
+			"hwIDAQAB\n" +
+			"-----END PUBLIC KEY-----";
+
+	private static final String VALID_AUTH_HEADER = "Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiJ9." +
+			"eyJzdWIiOiJ2YWxpZF91c2VyX2lkIiwiaWF0IjoxNzI5NjM0MjYwLCJuYmYiOjE3Mjk2MzQyNjAsImV4cCI6MzA1" +
+			"NTY4OTE1OTQwMzc0NTl9.xBL5BYiv8B-ZN1bCuljuJ7dZeOPocVPPVwkeK_GH4lD5iQqD08zi93WuXw1c6NWWCK4" +
+			"jn4ZssYrzSLLL5q3tAYbLKuhQ2-2A-e1HTasfvSnx_jCBUNApbIv3rM19M3rhRVRSxT2s2jI7dJFlM6E_bGMfj9w" +
+			"uoZiT_amjIIPQJiRkDKcO2sXnD6eU_yx8EIhH_PemSX3kp9Sx9eTYqGbyCtLrs9jK7nr6GQ_1jc6ie03Uh2dsIzW" +
+			"sZqGHh2n_WmdyURWEfwsMYFpepRLzm77dP9q78RgA8eDLZSLNW9ssJMYWY9DRkOZBFFuf4uy-uqC9MWS64DkJSAo" +
+			"nH8Zof_tUiQ";
+
+	private static final String VALID_USER_ID = "valid_user_id";
+
+	@BeforeEach
+	public void setUp() throws Exception {
+		jwtAuthorizer = new JwtAuthorizer(PUBLIC_KEY);
+		headers = mock(HttpHeaders.class);
+	}
+
+	@Test
+	public void testValidJwtToken() {
+		when(headers.getHeaderString(HttpHeaders.AUTHORIZATION)).thenReturn(VALID_AUTH_HEADER);
+
+		AuthResponse authResponse = jwtAuthorizer.verify(headers);
+
+		assertNotNull(authResponse);
+
+		assertEquals(VALID_USER_ID, authResponse.getUserToken());
+	}
+
+	@Test
+	public void testMissingAuthorizationHeader() {
+		when(headers.getHeaderString(HttpHeaders.AUTHORIZATION)).thenReturn(null);
+
+		assertThrows(AuthException.class, () -> jwtAuthorizer.verify(headers));
+	}
+
+	@Test
+	public void testInvalidAuthorizationHeader() {
+		when(headers.getHeaderString(HttpHeaders.AUTHORIZATION)).thenReturn("InvalidHeader");
+
+		assertThrows(AuthException.class, () -> jwtAuthorizer.verify(headers));
+	}
+
+	@Test
+	public void testInvalidJwtToken() {
+		String invalidJwt = "Bearer invalid.jwt.token";
+		when(headers.getHeaderString(HttpHeaders.AUTHORIZATION)).thenReturn(invalidJwt);
+
+		assertThrows(AuthException.class, () -> jwtAuthorizer.verify(headers));
+	}
+}