To get started, you must have a version of Delphi installed on your computer. For the examples, we will use Delphi Rio, but you can use your version of Delphi, provided it is from Seattle 10 or later.

The code files for this chapter are present on GitHub: https://github.com/PacktPublishing/Delphi-Programming-Projects/tree/master/Chapter02.

Delphi comes with all the components you need for you to enjoy this chapter. We will basically use the TRESTClient component to do this. First, you'll be taught how to authenticate with Facebook and get an access token, and then how to run an Open Graph query to get user information. Being able to authenticate on Facebook is very useful if you are creating any kind of content application for Android or iOS.

The Graph API is the key way to interact with the Facebook platform. It is a low-level API that uses applications to query data, publish new posts, manage ads, upload photos, and more.

The purpose of this chapter is to develop a hybrid application (Windows, Android, iOS, and macOS) that will connect to Facebook through the Graph API.

The estimated build time is 10 minutes.

You must have internet access to register your application on Facebook and consume the REST API.

You need to register your project as an application on Facebook before you can access the Facebook API using Delphi. We can do this using the following page: https://developers.facebook.com/apps. The page will look like the following screenshot:

We will create the application on the Facebook platform, which is necessary to perform the integration and log in on the Facebook platform for this project and follow these steps:

1. Add a new application to Facebook. For this chapter, we will call it DelphiProjectsPackt:

2. Solve the reCAPTCHA and Submit your information:

3. Navigate to Select a Scenario | Integrate Facebook Login:

4. Before saving changes, fill in the two required fields—Privacy Policy URL and Category:

5. Save the changes.
6. Click on Finish Quickstart, as shown in the following screenshot:

7. Select Web in Quickstart options...

REST is one of the main models that has been described by Roy Fielding, one of the principal creators of the HTTP protocol, in his Ph.D. thesis and adopted as the model to be used in the evolution of the HTTP protocol architecture.

The Embarcadero REST Library is accessible for all platforms, supported by Delphi.

The framework focuses on JSON as the representation format. The XML format is not supported.

The Embarcadero REST Library consists of three main components—the request, the client, and the response. All are part of a single workflow when submitting, processing, and returning the request with JSON.

This component performs a request to a REST server. TRESTClient...

JSON is an open standard file format that utilizes to convey data objects. These objects consist of attribute-value pairs and array data types. Delphi provides a native library for working with JSON containing classes and methods for storing, parsing, reading, writing, and generating data. Facebook works with JSON information traffic through the Graph API. When you use communication with Facebook's REST server, the expected return is the result of the JSON standard.

The following code snippet illustrates an example in JSON:

{
    "glossary": {
        "title": "example glossary",
    "GlossDiv": {
            "title": "S",
      "GlossList": {
                "GlossEntry": {
                    "ID": "SGML",
          "SortAs": "SGML",
        ...

You request an access token by opening the page. The access token is valid for only two hours. You can update the token in the background without the user having to log in again.

We have reached the last stage of this chapter. This is where we will add the final seasoning. To finally include the login functionality, you need to create a new form to receive a web page with which the user will interact to confirm their identity and to confirm the permissions requested by the application.

Before encoding the login, we need to create a new form to display the Facebook authentication Uniform Resource Identifier (URI). By following the next steps alongside the new form, we will finally be able...

In this chapter, we learned interesting concepts about REST APIs, authentication, security, and, of course, how to log in to one of the most popular social networks, Facebook.

The first step was to create a direct application on the Facebook platform, selecting the desired login type (login flow for web) and some other additional information, such as application name, permissions, and application ID, among others.

With the application ID in hand, we started building our Delphi application to interact using the REST component suite with Facebook.

It is noteworthy that, without the correct configuration of the components and following the technical standards of connection of the platform, none of this would be possible. The same goes for any REST API service that's available. Some will use OAuth2, like Facebook; others will not. What's important to note is the...

For more information about Facebook login types, including access permissions, go to https://developers.facebook.com/docs/facebook-login/manually-build-a-login-flow and https://developers.facebook.com/docs/facebook-login/permissions.