fixup! Add JWTAuthorizer Implementation.

Author: G8XSU

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

@@ -14,15 +14,22 @@
 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;
 
-	public static final String BEARER_PREFIX = "Bearer ";
+	private static final String BEARER_PREFIX = "Bearer ";
+	private static final int MAX_USER_TOKEN_LENGTH = 120;
 
-	public JwtAuthorizer(String pemFormatPublicKey) throws Exception {
-		this.publicKey = loadPublicKey(pemFormatPublicKey);
+	// `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();
@@ -47,6 +54,8 @@ public AuthResponse verify(HttpHeaders headers) throws AuthException {
 
 			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);
@@ -56,8 +65,8 @@ public AuthResponse verify(HttpHeaders headers) throws AuthException {
 		}
 	}
 
-	private PublicKey loadPublicKey(String pemFormatPublicKey) throws Exception {
-		String key = pemFormatPublicKey
+	private PublicKey loadPublicKey(String pemFormatRSAPublicKey) throws Exception {
+		String key = pemFormatRSAPublicKey
 				.replaceAll("\\n", "")
 				.replace("-----BEGIN PUBLIC KEY-----", "")
 				.replace("-----END PUBLIC KEY-----", "");