Refactor in jwtVendor 1

Signed-off-by: Ryan Liang <jiallian@amazon.com>

Author: RyanL1997

src/main/java/org/opensearch/security/authtoken/jwt/JwtVendor.java

@@ -116,22 +116,22 @@ public String createJwt(
         List<String> roles,
         List<String> backendRoles
     ) throws Exception {
-        long timeMillis = timeProvider.getAsLong();
-        Instant now = Instant.ofEpochMilli(timeProvider.getAsLong());
+        final long nowAsMillis = timeProvider.getAsLong();
+        final Instant nowAsInstant = Instant.ofEpochMilli(timeProvider.getAsLong());
 
         jwtProducer.setSignatureProvider(JwsUtils.getSignatureProvider(signingKey));
         JwtClaims jwtClaims = new JwtClaims();
         JwtToken jwt = new JwtToken(jwtClaims);
 
         jwtClaims.setIssuer(issuer);
 
-        jwtClaims.setIssuedAt(timeMillis);
+        jwtClaims.setIssuedAt(nowAsMillis);
 
         jwtClaims.setSubject(subject);
 
         jwtClaims.setAudience(audience);
 
-        jwtClaims.setNotBefore(timeMillis);
+        jwtClaims.setNotBefore(nowAsMillis);
 
         expirySeconds = (expirySeconds == null) ? 300 : expirySeconds;
         if (expirySeconds <= 0) {