allow to hide cancel-Button in authenticator view controller

so the user is stuck in authentication

Classes/BITAuthenticationViewController.h

@@ -19,6 +19,11 @@
  */
 @property (nonatomic, assign) BOOL requirePassword;
 
+/** configure if user can abort authentication or not
+ *
+ *  defaults to YES
+ */
+@property (nonatomic, assign) BOOL showsCancelButton;
 /**
  *	TODO: instead of passing the whole authenticator, we actually only need
  *        something to create and enqueue BITHTTPOperations

Classes/BITAuthenticationViewController.m

@@ -41,11 +41,8 @@
   
   _statusBarStyle = [[UIApplication sharedApplication] statusBarStyle];
   [[UIApplication sharedApplication] setStatusBarStyle:(self.navigationController.navigationBar.barStyle == UIBarStyleDefault) ? UIStatusBarStyleDefault : UIStatusBarStyleBlackOpaque];
-  
-  // Do any additional setup after loading the view.
-  self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemCancel
-                                                                                        target:self
-                                                                                        action:@selector(dismissAction:)];
+
+  [self updateCancelButton];
   
   self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemSave
                                                                                          target:self
@@ -60,6 +57,23 @@
   [[UIApplication sharedApplication] setStatusBarStyle:_statusBarStyle];
 }
 
+- (void)setShowsCancelButton:(BOOL)showsCancelButton {
+  if(_showsCancelButton != showsCancelButton) {
+    _showsCancelButton = showsCancelButton;
+    [self updateCancelButton];
+  }
+}
+
+- (void) updateCancelButton {
+  if(self.showsCancelButton) {
+    self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemCancel
+                                                                                          target:self
+                                                                                          action:@selector(dismissAction:)];
+  } else {
+    self.navigationItem.leftBarButtonItem = nil;
+  }
+}
+
 #pragma mark - UIViewController Rotation
 
 - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)orientation {