如何使用Keychain访问来存储iPhone App中的密码？

#import <Security/Security.h>

NSString *serviceIdentifier = @"com.example.app";
NSString *account = @"userAccount";
NSString *password = @"userPassword";

NSData *passwordData = [password dataUsingEncoding:NSUTF8StringEncoding];

NSMutableDictionary *query = [NSMutableDictionary dictionary];
[query setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];
[query setObject:serviceIdentifier forKey:(__bridge id)kSecAttrService];
[query setObject:account forKey:(__bridge id)kSecAttrAccount];
[query setObject:passwordData forKey:(__bridge id)kSecValueData];

OSStatus status = SecItemAdd((__bridge CFDictionaryRef)query, NULL);
if (status == errSecSuccess) {
    NSLog(@"Password saved to Keychain");
} else {
    NSLog(@"Failed to save password to Keychain");
}

NSString *serviceIdentifier = @"com.example.app";
NSString *account = @"userAccount";

NSMutableDictionary *query = [NSMutableDictionary dictionary];
[query setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];
[query setObject:serviceIdentifier forKey:(__bridge id)kSecAttrService];
[query setObject:account forKey:(__bridge id)kSecAttrAccount];
[query setObject:(__bridge id)kCFBooleanTrue forKey:(__bridge id)kSecReturnData];

CFTypeRef result = NULL;
OSStatus status = SecItemCopyMatching((__bridge CFDictionaryRef)query, &result);

if (status == errSecSuccess) {
    NSData *passwordData = (__bridge_transfer NSData *)result;
    NSString *password = [[NSString alloc] initWithData:passwordData encoding:NSUTF8StringEncoding];
    NSLog(@"Password retrieved from Keychain: %@", password);
} else {
    NSLog(@"Failed to retrieve password from Keychain");
}