1) I have a HOME screen in my iOS native application.
2) From there I have to navigate to Salesforce login screen.
3) User will enter credentials and Salesforce will validate it.
4) Once logged in success then it will back to my HOME screen with token/sessionID.
5) That token/sessionID I will use internally in my application.

- (IBAction)login:(UIButton*)sender {

    NSString *strClientID = @"2kN3Bn17hv5A1f.3QFK.....";
    NSString *strCallbackURI = @"https://localhost:0000/signin-salesforce";

    NSString *kIdentifier = @"com.salesforce.ios";

    SFOAuthCredentials *creds = [[SFOAuthCredentials alloc] initWithIdentifier:kIdentifier clientId:strClientID encrypted:YES];
    creds.redirectUri = strCallbackURI;

    _oauthCoordinator = [[SFOAuthCoordinator alloc] initWithCredentials:creds];
    // _oauthCoordinator.scopes = [NSSet setWithObjects: @"web", nil]; /* If I pass scopes then I'm getting "Invalid scopes even I enabled same scopes in salesforce as a connected app" */
    _oauthCoordinator.delegate = self;
    [_oauthCoordinator authenticate];
}

#pragma mark - SFOAuthCoordinatorDelegate

- (void)oauthCoordinator:(SFOAuthCoordinator *)manager didBeginAuthenticationWithView:(UIWebView *)webView {

    CGRect newFrame = self.view.frame;
    newFrame.origin.y +=64;
    webView.frame = newFrame;
    [self.view addSubview:webView];
}

- (void)oauthCoordinatorDidAuthenticate:(SFOAuthCoordinator *)coordinator authInfo:(SFOAuthInfo *)info
{
    [self.oauthCoordinator.view removeFromSuperview];
    NSLog(@"authType = %d",info.authType);
    NSLog(@"accessToken = %@",coordinator.credentials.accessToken);
    NSLog(@"refreshToken = %@",coordinator.credentials.refreshToken);
    NSLog(@"instanceUrl = %@",[coordinator.credentials.instanceUrl description]);
    NSLog(@"issuedAt = %@",[coordinator.credentials.issuedAt descriptionWithLocale:[NSLocale currentLocale]]);
    NSLog(@"userId = %@",coordinator.credentials.userId);
    NSLog(@"organizationId = %@",coordinator.credentials.organizationId);
    NSLog(@"communityId = %@",coordinator.credentials.communityId);
    NSLog(@"legacyIdentityInformation = %@",coordinator.credentials.legacyIdentityInformation);
    NSLog(@"activationCode = %@",coordinator.credentials.activationCode);
}

- (void)oauthCoordinator:(SFOAuthCoordinator *)coordinator didFailWithError:(NSError *)error authInfo:(SFOAuthInfo *)info
{

    [self.oauthCoordinator.view removeFromSuperview];
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:[NSString stringWithFormat:@"Error %d", error.code]
                                                    message:error.localizedDescription
                                                   delegate:nil
                                          cancelButtonTitle:@"OK"
                                          otherButtonTitles:nil];
    [alert show];
}

Output log
2014-12-19 12:55:45.946 SampeSalesforce[24576:607] authType = 1
2014-12-19 12:55:45.947 SampeSalesforce[24576:607] accessToken = MAQOGHGMlDR.keKCErM5MAIHJI65S5ABF646DBB89AB767FBAB77575l2Dbf4Z6UkdYnE8x70BoXLzP
2014-12-19 12:55:45.948 SampeSalesforce[24576:607] refreshToken = (null)
2014-12-19 12:55:45.948 SampeSalesforce[24576:607] instanceUrl = (null)
2014-12-19 12:55:45.948 SampeSalesforce[24576:607] issuedAt = (null)
2014-12-19 12:55:45.948 SampeSalesforce[24576:607] userId = (null)
2014-12-19 12:55:45.948 SampeSalesforce[24576:607] organizationId = (null)
2014-12-19 12:55:45.949 SampeSalesforce[24576:607] communityId = (null)
2014-12-19 12:55:45.949 SampeSalesforce[24576:607] legacyIdentityInformation = (null)