fix: removed noauth flow (#899)

* removed noauth flow

* added noauth test

Author: sbansla

src/main/java/com/twilio/TwilioNoAuth.java

@@ -2,9 +2,24 @@
 
 import com.twilio.constant.EnumConstants;
 
+// Does not have any state thus thread safe.
 public class NoAuthStrategy extends AuthStrategy {
+    private static volatile NoAuthStrategy INSTANCE;
 
-    public NoAuthStrategy(String token) {
+    private static volatile NoAuthStrategy instance;
+
+    public static NoAuthStrategy getInstance() {
+        if (instance == null) {
+            synchronized (NoAuthStrategy.class) {
+                if (instance == null) {
+                    instance = new NoAuthStrategy();
+                }
+            }
+        }
+        return instance;
+    }
+
+    private NoAuthStrategy() {
         super(EnumConstants.AuthType.NO_AUTH);
     }
 

src/main/java/com/twilio/auth_strategy/NoAuthStrategy.java

@@ -89,10 +89,13 @@ protected TwilioRestClient(Builder b) {
      * @return Response object
      */
     public Response request(final Request request) {
-        if (username != null && password != null) {
-            request.setAuth(username, password);
-        } else if (authStrategy != null) {
-            request.setAuth(authStrategy);
+        // If authStrategy is passed from NoAuth API, no need to set authStrategy (ex TokenCreator). 
+        if (request.getAuthStrategy() == null) {
+            if (username != null && password != null) {
+                request.setAuth(username, password);
+            } else if (authStrategy != null) {
+                request.setAuth(authStrategy);
+            }
         }
 
         if (region != null)