Login and Password Input with NSURLConnection - ios

Question

I am a newbie in the development of iOS applications.
I need to reach different url loaded from a remote XML file,
some of these url require a http basic authentication.
Authentication with NSURLCredential, it works correctly.
Now, I want to require the user to enter their credentials.
When the connection fails I visualize the interface
login UIAlertView with setAlertViewStyle:UIAlertViewStyleLoginAndPasswordInput.
At this point I verify the correspondence
username and password entered by the user with textFieldAtIndex: 0 and 1
but I can and use them for a new connection attempt with NSURLConnection.
Can someone help me?
This is my code:
- (void)connection:(NSURLConnection *)connection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge {
if ([challenge previousFailureCount] == 0)
{
NSLog(#"received authentication challenge");
NSURLCredential *newCredential;
newCredential=[NSURLCredential credentialWithUser:#""
password:#""
persistence:NSURLCredentialPersistenceForSession];
NSLog(#"credential created");
[[challenge sender] useCredential:newCredential forAuthenticationChallenge:challenge];
NSLog(#"responded to authentication challenge");
}
else
{
NSLog(#"previous authentication failure");
UIAlertView *message = [[UIAlertView alloc] initWithTitle:#"Login"
message:#"Enter your username & password"
delegate:self
cancelButtonTitle:#"Cancel"
otherButtonTitles:#"Login", nil];
[message setAlertViewStyle:UIAlertViewStyleLoginAndPasswordInput];
[message show];
}
}
- (BOOL)alertViewShouldEnableFirstOtherButton:(UIAlertView *)alertView
{
NSString *inputText = [[alertView textFieldAtIndex:0] text];
if( [inputText length] >= 1 )
{
return YES;
}
else
{
return NO;
}
}
- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
NSString *title = [alertView buttonTitleAtIndex:buttonIndex];
if([title isEqualToString:#"Login"])
{
UITextField *username = [alertView textFieldAtIndex:0];
UITextField *password = [alertView textFieldAtIndex:1];
NSLog(#"Username: %#\npassword: %#", username.text, password.text);
if ([username.text isEqualToString:#"myname"] && [password.text isEqualToString:#"1234"])
NSLog(#"Success");
}
[xmlDataBuffer setLength:0];
}