-(void)connection:(NSURLConnection *)aConnection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge {
        if ([challenge previousFailureCount] == 0) {
                NSURLCredential *newCredential;
                newCredential = [NSURLCredential credentialWithUser:username password:password persistence:NSURLCredentialPersistenceNone];
                [[challenge sender] useCredential:newCredential forAuthenticationChallenge:challenge];
        } else {
                [[challenge sender] cancelAuthenticationChallenge:challenge];
        }
}