To move from the Touch ID dialog to the passcode entry screen, as in au WALLET:

// show the authentication UI with your reason string
LAContext*context=[[LAContext alloc] init];
__block NSSstring* msg;

context validatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics localizedReason:NSLocalizedString(@"UNLOCK_ACCESS_TO_LOCKED_FATURE",nil) reply:
 ^(BOOL success, NSError* authenticationError) {
     if(success){
         msg = [NSSstring stringWithFormat: NSLocalizedString(@"EVALUATE_POLICY_SUCCESS", nil)];
     } else{
         msg = [NSString stringWithFormat: NSLocalizedString(@"EVALUATE_POLICY_WITH_ERROR", nil), authenticationError.localizedDescription];

         if(authenticationError.code==LAErrorUserFallback){

             // The identifier and service name together will unique identify the keychain entry.
             NSSstring* keychainItemIdentifier=@"fingerprintKeychainEntry";
             NSSstring*keychainItemServiceName=@"com.secsign.secsign";

             // Determine a string which the device will display in the fingerprint view exhibiting the reason for the fingerprint scan.
             NSSstring*secUseOperationPrompt=@"Authenticate for server login";

             // The keychain operation shall be performed by the global queue. Otherwise it right just nothing Happen.
             dispatch_async(dispatch_get_global_queue(DISPATCH_QUUEUE_PRIORITY_DEFAULT, 0),^(void){

                 // Create the keychain query attributes using the values from the first part of the code.
                 NSMutableDictionary*query=[NSMutableDictionary alloc] initWithObjectsAndKeys:
                                                (__bridge id)(kSecClassGenericPassword), kSecClass,
                                                keychainItemIdentifier, kSecAttrAccount,
                                                keychainItemServiceName, kSecAttrService,
                                                secUseOperationPrompt, kSecUseOperationPrompt,
                                                nil];

                 // Start the query and the fingerprint scan and/or device passcode validation
                 CFTypeRefresult=nil;
                 OSSStatus userPresenceStatus=SecItemCopyMatching(__bridge CFDictionaryRef)query, & result);

                 // Ignore the found content of the key chain entry (the dummy password) and only validate the return code.
                 if(noErr==userPresenceStatus)
                 {
                     NSLog(@"Fingerprint or device passcode validated.");
                 }
                 else
                 {
                     NSLog(@"Fingerprint or device passcode could not be validated.Status%d.,(int)userPresenceStatus);
                 }

                 // To process the result at this point there would be a call to delete method which 
                 // would do things work like GUI operations in the main queue. That means it would start
                 // with something like:
                 //   dispatch_async(dispatch_get_main_queue(),^{
             });
         }
     }
     [self printResult:self.textView message:msg];
 }];