- API Penetration Testing

9 Open-Source API Security Testing & Manipulation Tools

Learn about top open-source API security testing and manipulation tools that are worth considering in 2022
The earlier you catch software bugs, the easier and cheaper it is to fix them. "Test early and often" is the mighty mantra in the contemporary software testing circuit."

In practice, this means tying the quality assurance practice with your development process, so the two work synergistically and are in the same loop at all times. More importantly, in this "shift-left" approach, quality assurance engineers are involved more intensely and earlier on in your project. Since processes run in parallel, the savings on your project are enormous in terms of calendar time, staff strength, and testing infrastructure. However, there are still some loose ends.

The manual user interface (UI) testing involved here was conceived in the bygone era of monolithic applications. Microservices apps and APIs increasingly represent the new world order in the software realm and API testing is proving very crucial. Old-world UI testing, although still relevant, is certainly not good enough to meet the rigors of API testing.

Of late, some automated UI testing tools have appeared in the market and early responses from users are quite encouraging. These applications leverage AI and its pattern recognition capabilities as well as machine learning to convert manual UI testing into API tests. By so doing, they validate APIs based on how well they meet user expectations around functionality, reliability, performance, and security.

Here's looking at some of the top trending API security testing tools in the market and all of these are open source:
#1 REST-Assured
REST-Assured is a Java-based library used to test APIs conforming to the REST web-standards-based architecture. The library in this case is Fluent, which is ultra-lightweight and supports the design of APIs that are more domain-specific as well as intuitive for users.

If you have so many basic Java skills, with REST-Assured, it shouldn't be difficult to send "simple" http requests (i.e., requests which don't trigger preflight requests). The test cases for validating your application's behavior/functionality are written in natural language that even your business users can read and interpret. Coding in Java can be a stumbling block for non-programmers. No worries. REST-Assured, with its numerous built-in functionalities, spares you the pain of Java coding. The tool essentially simplifies the testing of REST services in Java and, in this respect, puts Java on an equal footing with dynamic programming languages (e.g., Ruby, Groovy). REST-Assured is highly recommended if your teams use Java for the most part.
#2 Postman
Postman is a handy and scalable tool for testing REST APIs, apart from building and modifying them. It is also a great tool for performing exploratory testing of APIs to bring to light hidden risks. This scalable REST API client is capable of sending complex requests with different body types (URL-encoded, multipart/form-data, raw body, binary data). Based on request settings, Postman will automatically append certain headers to your requests as well as enable syntax highlighting. The tool comes with an automatic language detection option, which simplifies the process of verifying API responses (namely, body, headers, status code). Postman also lets you generate pre-developed scripts ("snippets) in various languages and frameworks to perform automated verification of APIs. You can easily check these responses and response time/size via the Postman native apps that run on Windows, Mac, and Linux. Postman eliminates the need to manually input the authorization token (OAuth) for each API. Overall, the tool irons out the API lifecycle at every stage, including testing and deployment.
#3 Hoppscotch
Hoppscotch (previously "Postwoman") was developed by Liyas Thomas, sometime in 2019, initially as a Web-based substitute to Postman. Built on Chromium browser, this open-source API request builder will help speed API requests faster and save you development time. The UI design is minimalist and function-oriented with a lightweight framework. Hoppscotch carries the advantage of being able to run cross platform. This contrasts with Postman, which has separate builds written using Electron framework, without which the tool cannot run cross-platform. Besides, you can access Hoppscotch from anywhere since it is online and you don't need to go through all the hassle of installing the software. Ease of use and customizability are some of Hoppscotch's high points, and the tool will likely be feature-enriched further in the days ahead. Since August 2019, this open-source project has attracted 35,000 stars on GitHub, an indication of its growing popularity with developers.
#4 SoapUI
This is a user-friendly open-source tool for performing security, compliance, functional, and load testing on your APIs and web services. The security testing features will help provide a secure API environment for your target services, especially the more vulnerable public-facing apps. You can use existing test cases on SoapUI or create and run test cases for validating specific API functions or other features you have in mind. Each security test suite might include multiple test cases and test steps at the next level, apart from multiple security scans (e.g., malicious attachment, SQL injection, XML Bomb). SoapUI will help you keep an eye on each test step in every single test case. The test results take the form of security logs, which provide details on failed security scans as well as alerts on potential security vulnerabilities. You can also define arbitrary functionalities in test cases by executing script code using Groovy Script TestStep.
#5 JMeter
Apache JMeter was created primarily for performance testing of web applications but has since proved to be highly effective in functionality/reliability/security testing as well. The tool also integrates with your Jenkins pipeline to enable faster software development and deployment. JMeter is purely Java-based and can execute on a Java Virtual Machine (JVM) across platforms (Windows, Linux, macOS). The multithreading framework allows simultaneous sampling of different API functions by several threads and thread groups. JMeter has a straightforward and intuitive GUI capable of visualizing test results in the form of charts, tables, trees, and log files. The tool can easily pick data from various data sets (CSV, HTML, JSON, XML). This will help your teams to quickly create values of API parameters. The Apache core is highly extensible, which means you can expand the scope of your testing by writing custom tests and using plugins. Overall, JMeter supports rapid and hassle-free API validation.
#6 Karate
Karate unifies API test automation, performance testing, and UI automation in a single end-to-end framework and allows even non-techies to contribute to the testing activity. This framework also provides for API test doubles ("mocks") of dependencies that are still in development or otherwise unavailable. The other advantage is that Karate doesn't require you to create step definitions and describe the specifications that the testing framework must work through. Unlike other behavior-driven development (BDD) frameworks, (Cucumber, JBehave, SpecFlow) Karate comes with such step definitions glued to the code, so you can start your API testing instantly! Though Karate is a Java-only framework, the test cases are written in language-neutral Gherkin. So, even non-programmers can run this tool with surprising ease. Even if your team is not so much into Java-based development, you will still find Karate useful. Because Karate's stand-alone executable file works cross-platform via a CLI.
#7 Fiddler
Fiddler is a popular testing tool for monitoring all of the network traffic ("http" and "https traffic") between the Internet and test APIs, both web and desktop. This free tool for macOS, Windows, and Linux is capable of not only discovering but also playing back requests from individual APIs to, say, a server-side application, thus helping debug web applications. The API Test Fiddler extension greatly enhances its power to execute and validate the behavior of web APIs. The tool can be extended to collect performance statistics on the client application (e.g., requests, response time, response size) as well as perform load testing. Moreover, with Fiddler, you don't need any extra skills to prepare and run load tests, so you save on skilled talent and pricey testing environments. Developers can easily introduce new features and desired behaviors on the go in Fiddler since the script underlying the tool is a .NET version of JavaScript that most of them are quite comfortable with.
#8 Insomnia
This free and user-friendly REST API client is used to store, organize, and send REST API requests elegantly. You can also create GraphQL requests in Insomnia without much effort. Insomnia provides a great way to group, share, and organize your cartload of requests elegantly. There are request collections at the first level and folders at the next level and you can use them either singly or in combination. Much like your web browser, Insomnia stores cookies from every web server response and sends them automatically with requests as required. It also allows you to reuse environmental variables (e.g., the consistent part of a URL) across multiple requests. Besides, this graphical tool will help you generate code snippets for at least 12 different languages as well as simplify the way you authenticate to the API via various authentication helpers. It's available for Windows, Mac, and Linux.
#9 Citrus
This open-source testing framework, written in Java, can help you run automated integrated tests on your enterprise applications. Citrus has virtually all message transport protocols and data formats covered. Kafka, Http REST, JMS, TCP/IP, SOAP, FTP/SFTP, SSH…you name it! The test case descriptions, which detail what is being verified, are created in Java or XML. Incoming and outgoing messages are predefined in the test case. You can execute the tests multiple times and the tests blend seamlessly into your continuous integration landscape. Citrus is particularly adapted to the testing requirements of "API-first" (headless) environments in which the back-end of the application is decoupled from the client-facing end and information exposed via APIs. The Citrus test framework comes with a good deal of supporting documentation on effective integration testing.
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