December 13 2009

System Preferences Pane Lock

by Brian Dunagan

Many panes in System Preferences require I authenticate myself to change settings. Apple has a consistent UI for this: the lock icon. Next to it is a little snippet of text telling me why it's useful: "Click the lock to make changes." I click it and authenticate, and it opens, enabling various buttons and fields in that pane. "Click the lock to prevent further changes." I click it again, and it locks, disabling those buttons and fields. This UI and underlying authentication process are included in Cocoa: SFAuthorizationView.

This tutorial creates a simple prefpane with a button and the lock UI, building on two earlier posts about root-level operations and debugging prefpanes. Clicking the button creates an empty file at /var/log/test.txt, an action that requires root-level privilege. The button is grayed out if the lock is locked; it enables when I unlock the lock. The source code for this project is available on Google Code.

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Xcode

1. To start, create a new Xcode project for a PreferencePane, listed in "Standard Apple Plug-ins".
2. Add the following frameworks to the project: Security and SecurityInterface.
3. In the header file, import the SecurityInterface framework and add two IBOutlets:

   #import <PreferencePanes/PreferencePanes.h>
   #import <SecurityInterface/SFAuthorizationView.h>
   
   @interface BDAuthorizePrefPanePref : NSPreferencePane  {
   	IBOutlet SFAuthorizationView *authView;
   	IBOutlet NSButton *touchButton;
   }
   
   - (BOOL)isUnlocked;
   - (IBAction)clickTouch:(id)sender;
   
   @end

4. In the source file, setup the security interface and handle its actions:

   #import "BDAuthorizePrefPanePref.h"
   
   @implementation BDAuthorizePrefPanePref
   
   - (void) mainViewDidLoad {
   	// Setup security.
   	AuthorizationItem items = {kAuthorizationRightExecute, 0, NULL, 0};
   	AuthorizationRights rights = {1, &items};
   	[authView setAuthorizationRights:&rights];
   	authView.delegate = self;
   	[authView updateStatus:nil];
   
   	[touchButton setEnabled:[self isUnlocked]];
   }
   
   - (BOOL)isUnlocked {
   	return [authView authorizationState] == SFAuthorizationViewUnlockedState;
   }
   
   - (IBAction)clickTouch:(id)sender {
   	// Collect arguments into an array.
   	NSMutableArray *args = [NSMutableArray array];
   	[args addObject:@"-c"];
   	[args addObject:@" touch /var/log/test.txt"];
   
   	// Convert array into void-* array.
   	const char **argv = (const char **)malloc(sizeof(char *) * [args count] + 1);
   	int argvIndex = 0;
   	for (NSString *string in args) {
   		argv[argvIndex] = [string UTF8String];
   		argvIndex++;
   	}
   	argv[argvIndex] = nil;
   
   	OSErr processError = AuthorizationExecuteWithPrivileges([[authView authorization] authorizationRef], [@"/bin/sh" UTF8String], 
   															kAuthorizationFlagDefaults, (char *const *)argv, nil);
   	free(argv);
   
   	if (processError != errAuthorizationSuccess)
   		NSLog(@"Error: %d", processError);
   }
   
   //
   // SFAuthorization delegates
   //
   
   - (void)authorizationViewDidAuthorize:(SFAuthorizationView *)view {
   	[touchButton setEnabled:[self isUnlocked]];
   }
   
   - (void)authorizationViewDidDeauthorize:(SFAuthorizationView *)view {
   	[touchButton setEnabled:[self isUnlocked]];
   }
   
   @end

   </ol>

   Interface Builder

   
   1. Open the xib file in the Resources folder of the new project.
   2. Change the NSFileOwner's class to the main controller's class.
   3. Resize the window to W:440,H:120.
   4. Drop an NSView into the content view of the window.
   5. Resize the view to X:20,Y:20,W:400,:H:40.
   6. Change the view's class to SFAuthorizationView.
   7. Place an NSButton above the security view and link its action to clickTouch:.
   8. Link up the outlets for the button and the security view. </ol>