Providing an option of login with Google plus is useful for your website and users because most people have Google plus account and they don't need to create one more account for your website. And also chance of your users enrolling for your website restricted features will increase with Google plus login option.
In your mobile app or website, there could be certain features or functionalities which are available to registered users only. In that case, you need to provide capability for users to do registration or sign up for those features.
Displaying content based on device screen size helps improve readability of any web page. With responsive design page content can be displayed based on screen size using @media rules in CSS. If you have requirement to display content only in two formats one for desktop screens and other one for mobile and table screens, you can create two versions of pages for desktop and small screens.
Facebook provides API to get data from Facebook and publish data to Facebook. If you own a business and want to interact with customers on Facebook, posting messages using tools , which rely on Facebook API, saves time and resources.
Without search functionality it is very hard for users of your website to find information they are looking for. There are several ways in which search functionality can be implemented.
If you can derive useful Twitter messages or data from your application database, there is no need to login to Twitter and post messages manually to communicate with your Twitter users. Automating message posting to Twitter not only helps save resources but it also helps in posting accurate messages provided you have right source of data which you want to communicate to your Twitter Users.
Emails are still a best way to communicate with users or customers to keep them up to date with news, offers, new features, products & services. Giving an option for users to enroll for news letters from the day one is a good marketing strategy for companies to accumulate list of email addresses which can be used to communicate news and offers with users.
Remote API can be used to access services on Google app engine from other java applications. It lets you access from your local machine such services as datastore and search etc. Since it lets you access server side resource, it needs proper access credentials (Google cloud account credentials) to perform those actions.
In web applications, sessions help track users activities and store data between the requests. Most of the application servers use memory to store session objects. But Google App Engine stores session data in datastore.
Most of the web applications contain secure content and non secure content. Secure content is shown to authenticated users with appropriate authorization for viewing such content. Without transport level security, confidential content is not fully protected from unauthorized access. In addition to authentication and authorization, transport level security is important to protect content from unauthorized access.