perf: Skip registering auth delegate if it's already registered (#1715)

Author: mtrezza

Parse/Parse/Internal/User/AuthenticationProviders/Controller/PFUserAuthenticationController.m

@@ -56,12 +56,19 @@ - (void)registerAuthenticationDelegate:(id<PFUserAuthenticationDelegate>)delegat
     PFParameterAssert(delegate, @"Authentication delegate can't be `nil`.");
     PFParameterAssert(authType, @"`authType` can't be `nil`.");
 
-    // If auth delete is already registered then unregister it gracefully
+    // If auth delete is already registered for provider
     if ([self authenticationDelegateForAuthType:authType]) {
+        
+        // If same auth delete is already registered then don't register it again
+        if ([self authenticationDelegateForAuthType:authType] == delegate) {
+            NSLog(@"skipping registering as same delegate already registered for authType `%@`.", authType);
+            return;
+        }
+        
         NSLog(@"unregistering existing deletegate to gracefully register new delegate for authType `%@`.", authType);
         [self unregisterAuthenticationDelegateForAuthType:authType];
     }
-    
+             
     dispatch_sync(_dataAccessQueue, ^{
         self->_authenticationDelegates[authType] = delegate;
     });