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Minimum Deployment Target

macOS 10.8 or later

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Platform Differences

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No Accessibility Types

Unlike iOS, macOS does not support the accessibilityType methods. These methods are wrapped in #if __IPHONE_4_0 && TARGET_OS_IPHONE directives and are not available on macOS. 
// These methods are NOT available on macOS:
// [SAMKeychain setAccessibilityType:...];  // iOS only
// [SAMKeychain accessibilityType];         // iOS only

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Access Groups

Access groups are available on macOS 10.9 and later, allowing keychain sharing between apps from the same developer. 
SAMKeychainQuery *query = [[SAMKeychainQuery alloc] init];
query.service = @"MyService";
query.account = @"user@example.com";
query.password = @"myPassword";
query.accessGroup = @"TEAM_ID.com.example.shared";

NSError *error = nil;
[query save:&error];

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iCloud Keychain Synchronization

iCloud Keychain synchronization is available on macOS 10.9 and later. 
// Check if synchronization is available at runtime
if ([SAMKeychainQuery isSynchronizationAvailable]) {
    SAMKeychainQuery *query = [[SAMKeychainQuery alloc] init];
    query.service = @"MyService";
    query.account = @"user@example.com";
    query.password = @"myPassword";
    query.synchronizationMode = SAMKeychainQuerySynchronizationModeYes;
    
    NSError *error = nil;
    [query save:&error];
}
The runtime check uses NSFoundationVersionNumber10_8_4 as the threshold. Items created on macOS 10.9+ can sync with iOS 7.0+ devices when synchronization is enabled.

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Delete Operation Behavior

macOS has special handling for delete operations due to platform-specific keychain behavior.
On macOS, SecItemDelete will not delete a key created in a different app, nor in a different version of the same app. This was true in OS X 10.6 and later versions.SAMKeychain works around this by using SecItemCopyMatching and SecKeychainItemDelete instead of the standard SecItemDelete. See SAMKeychainQuery.m:80-106 for implementation details.
// Delete operations work the same from the API perspective,
// but use a different implementation on macOS
BOOL success = [SAMKeychain deletePasswordForService:@"MyService" 
                                             account:@"user@example.com"];

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Error Handling

macOS uses SecCopyErrorMessageString for error messages, which provides more detailed system-level error information compared to the custom error messages used on iOS. 
NSError *error = nil;
BOOL success = [SAMKeychain setPassword:@"myPassword" 
                             forService:@"MyService" 
                                account:@"user@example.com" 
                                  error:&error];

if (!success) {
    NSLog(@"Error: %@", error.localizedDescription);
    // macOS error messages come from SecCopyErrorMessageString
}
See SAMKeychainQuery.m:303-306 for the macOS error handling implementation.

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Basic Usage

The standard keychain operations work the same as on other platforms: 
// Save a password
[SAMKeychain setPassword:@"myPassword" 
              forService:@"MyService" 
                 account:@"user@example.com"];

// Retrieve a password
NSString *password = [SAMKeychain passwordForService:@"MyService" 
                                             account:@"user@example.com"];

// Delete a password
[SAMKeychain deletePasswordForService:@"MyService" 
                              account:@"user@example.com"];

// Get all accounts for a service
NSArray *accounts = [SAMKeychain accountsForService:@"MyService"];

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Cross-Platform Considerations

When building apps for both iOS and macOS:
  1. Don’t use accessibility types - These are iOS-only
  2. Check synchronization availability - Different OS versions have different requirements
  3. Test delete operations - macOS has different behavior
  4. Access groups - Available on both platforms but with different minimum OS versions