iOS8之後蘋果發布了指紋識別的功能，通過touch ID來識別用戶，做用戶授權，主要是依賴於LocalAuthentication庫

指紋識別：一判斷設備是否支持指紋識別功能

二識別指紋，成功後做相應的動作，失敗後提醒用戶指紋識別失敗

先引入#import <LocalAuthentication/LocalAuthentication.h>

LAContext *context = [[LAContext alloc] init];
  NSError *error = nil;
  //驗證是否支持指紋識別
  if ([context canEvaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics error:&error]) {
    NSLog(@"支持指紋識別的應用");
    //驗證身份
    [context evaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics localizedReason:NSLocalizedString(@"需要指紋來驗證你的身份", @"hello") reply:^(BOOL success, NSError *error) {
      if (success) {
        NSLog(@"成功");
      } else {
        switch (error.code) {
          case LAErrorUserCancel:
            NSLog(@"用戶取消了授權 - %@", error.localizedDescription);
            break;
          case LAErrorUserFallback:
            NSLog(@"用戶點擊了“輸入密碼”按鈕 - %@", error.localizedDescription);
            break;
          case LAErrorAuthenticationFailed:
            NSLog(@"您已授權失敗3次 - %@", error.localizedDescription);
            break;
          case LAErrorTouchIDLockout:
            NSLog(@"指紋被鎖定 - %@", error.localizedDescription);
            break;
          case LAErrorSystemCancel:
            NSLog(@"應用程序進入後台 - %@", error.localizedDescription);
            break;
          default:
            NSLog(@"++%@--%zd", error.localizedDescription, error.code);
            break;
        }
      }
    }];
  } else {
    switch (error.code) {
      case LAErrorPasscodeNotSet:
        NSLog(@"未設置密碼 - %@", error.localizedDescription);
        break;
      case LAErrorTouchIDNotEnrolled:
        NSLog(@"未注冊 Touch ID - %@", error.localizedDescription);
        break;
      case kLAErrorTouchIDNotAvailable:
        NSLog(@"該設備不支持 Touch ID - %@", error.localizedDescription);
        break;
      default:
        NSLog(@"--%@--%zd", error.localizedDescription, error.code);
        break;
    }
  }