Using XAuth to exchange username/password credentials for a OAuth access token

gistfile1.m

// UITextFieldDelegate method, called when the "Return" key is pressed.
// Either advance the cursor to the next empty field, or submit the form.
//
- (BOOL)textFieldShouldReturn:(UITextField *)textField {
    if([usernameField.text length] == 0) {
        [usernameField becomeFirstResponder];
    } else if ([passwordField.text length] == 0) {
        [passwordField becomeFirstResponder];
    } else {
        [textField resignFirstResponder];
        [self getAccessToken];
    }
    
    return YES;
}

// Given a username and password, request an access token via XAuth and display
// a "loading" overlay box.
//
- (void)getAccessToken {
    OAConsumer *consumer = [[[OAConsumer alloc] initWithKey:consumerKey secret:consumerSecret] autorelease];
    NSURL *URL = [NSURL URLWithString:authURLString];
    OAMutableURLRequest *request = [[[OAMutableURLRequest alloc] initWithURL:URL consumer:consumer token:nil realm:nil signatureProvider:nil] autorelease];
    [request setHTTPMethod:@"POST"];
    [request setParameters:[NSArray arrayWithObjects:
        [OARequestParameter requestParameter:@"x_auth_mode" value:@"client_auth"],
        [OARequestParameter requestParameter:@"x_auth_username" value:self.usernameField.text],
        [OARequestParameter requestParameter:@"x_auth_password" value:self.passwordField.text],
        nil
    ]];
    
    OADataFetcher *dataFetcher = [[[OADataFetcher alloc] init] autorelease];
    [dataFetcher fetchDataWithRequest:request delegate:self didFinishSelector:@selector(setAccessToken:withData:) didFailSelector:@selector(accessTokenTicket:didFailWithError:)];
    
    [loadingOverlay setText:NSLocalizedString(@"Authorizing", nil)];
    [loadingOverlay showAnimated:YES];
}

// If the token request fails, alert the user.
//
- (void)accessTokenTicket:(OAServiceTicket *)ticket didFailWithError:(NSError *) error {
    [loadingOverlay hideAnimated:YES];
    NSString *title = NSLocalizedString(@"Authorization Failed", nil);
    NSString *message = NSLocalizedString(@"Check your username and password", nil);
    NSString *cancelTitle = NSLocalizedString(@"Close", nil);
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:title message:message delegate:nil cancelButtonTitle:cancelTitle otherButtonTitles:nil];
    [[alertView autorelease] show];
}

// If the token request succeeds, handle the response. (A successful HTTP request doesn't
// necessarily imply a token was successfully generated).
//
- (void)setAccessToken:(OAServiceTicket *)ticket withData:(NSData *)data {
    if (!ticket.didSucceed || !data) {
        [self accessTokenTicket:ticket didFailWithError:nil];
        return;
    }
    
    NSString *dataString = [[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] autorelease];
    if (!dataString) {
        [self accessTokenTicket:ticket didFailWithError:nil];       
        return;
    }
    
    NSArray *dataStringComponents = [dataString componentsSeparatedByString:@"&"];
    
    for(NSString *string in dataStringComponents) {
        NSRange range = [string rangeOfString:@"oauth_token=" options:NSLiteralSearch];
        if (range.location != NSNotFound) {
            self.authToken = [string substringWithRange:NSMakeRange(range.location + range.length, [string length] - range.length)];
        }
    }
    
    for(NSString *string in dataStringComponents) {
        NSRange range = [string rangeOfString:@"oauth_token_secret=" options:NSLiteralSearch];
        if (range.location != NSNotFound) {
            self.authSecret = [string substringWithRange:NSMakeRange(range.location + range.length, [string length] - range.length)];
        }
    }
    
    [loadingOverlay setText:NSLocalizedString(@"Saving", nil)];
    [self saveToken];
}

// If a token was received, save it to the Gowalla server.
//
- (void)saveToken {
    NSMutableDictionary *params = [NSMutableDictionary dictionary];
    [params setObject:authToken forKey:@"token"];
    [params setObject:authSecret forKey:@"secret"];
    [AFHTTPRequest post:saveTokenURL params:params delegate:self successSelector:@selector(requestDidSucceed:)];
}

// If saving the token failed, alert the user
//
- (void)request:(AFHTTPRequest *)request didFailWithError:(NSError *)error {
    [loadingOverlay hideAnimated:YES];
    NSString *title = NSLocalizedString(@"Saving Failed", nil);
    NSString *message = NSLocalizedString(@"Your authorization couldn’t be saved", nil);
    NSString *cancelTitle = NSLocalizedString(@"Close", nil);
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:title message:message delegate:nil cancelButtonTitle:cancelTitle otherButtonTitles:nil];
    [[alertView autorelease] show];
}

// If saving the token succeeded, return to the parent controller.
//
- (void)requestDidSucceed:(AFHTTPRequest *)request {
    [loadingOverlay hideAnimated:YES];
    [self.navigationController popViewControllerAnimated:YES];
}