Strong APIs can help protect your UI from unauthorized access to customer data, backend server appliances, and even monetary systems. Weak points in an API construct can expose these sensitive areas to attackers, putting your business at risk. Proper coding practices, such as proper error handling, value checking, and memory overflow prevention can help prevent these vulnerabilities.
Some common API vulnerabilities include Broken Object Level Authorization (BOLA), Broken User Authentication, Improper Asset Management, Excessive Data Exposure, Lack of Resources & Rate Limiting, Broken Function Level Authorization, Mass Assignment and Injection. These vulnerabilities can expose sensitive data and leave your system open to attacks. Soit’s important to understand and address these vulnerabilities to keep your API secure. Let us understand how strong API’s can make your UI less vulnerable!
What is API?
API stands for application programming interface, which is a set of definitions and protocols for building and integrating software. It is a software-to-software interface, a language through which software talks to each other by writing function calls in the program. In other words, a set of commands used by an individual program to communicate with one another directly and use each other’s functions to get information.
What is API testing?
API testing is the process of sending requests to an API and monitoring the responses to ensure it is behaving as expected. API testing is designed to assess the functionality, reliability, performance, and security of an API, and is an essential part of the Software development lifecycle.
Software application development is dominated by the three-layered architecture approach, which is an architecture made up of a presentation layer, business logic layer, and database layer.
The business logic layer contains the core functionality, or components, of the application. It must take information fed by the user from the presentation layer, query the database layer and transform that data according to the business logic, and present the results back to the user via the presentation layer. But the business logic layer must also communicate with other applications as well as human users. To do so, it uses an API.
Hence it is designed to validate the business logic as well as the functionality, reliability, performance, and security of an API, and is an essential part of the software development lifecycle.
Why is API Testing required?
API testing is important for ensuring that your API performs as expected when faced with a wide variety of expected and unexpected requests. This process is designed to not only test the API’s functionality — but also its reliability, performance, and security. 
API testing is also important because it offers several advantages over other types of testing, like unit and UI testing.
For example, unit tests are designed to verify the functionality of individual components within a single application whereas API tests are designed to verify that all system components function as intended. This broader test coverage makes it easier to identify any bugs in the unit, database, and server levels.
API tests are also faster to run and more isolated than UI tests, which makes it quicker and easier to identify and resolve bugs. According to research, a UI test runs for approximately seven minutes while an API test runs for 12 seconds. Meaning, an API test is about 35 times faster than a UI test.
Perhaps most importantly, API testing allows developer operations, quality assurance, development, and other teams to begin testing an application’s core functionality before the user interface is ready. This enables them to identify any errors or weaknesses early on in the development process. If identified later in the process, these errors and weaknesses in the build can be costly to fix, requiring large amounts of code to be rewritten and significantly delaying the product’s release.
How to do API testing?
There are a few parameters that allow us to perform API testing, let us discuss some of them:
Review the API specification
Before you start testing, you need to first understand the purpose of the API, how the API functions, and what results to expect when using the API. To do so, you can review the API specification.
Suppose you’re testing an HTTP API then the specification details all the HTTP API’s objects, values, and parameters, how the objects are called, what each object does, and how they can be used together.
Let's take an example of a simple web application accepting User registration now we want to test the User Registration API.
In which the registration form takes User's First Name, last name, Email ID, and Phone number as input values.
So, if we want to validate the create User API then in that case the API specifications would be:
Request type: - Post
Request Body: - contains following field First Name, Last Name, email id, and alternate email idDefine API Testing requirements
This requires a proper understanding of the features, functionality, and workflow of the Application. Certain parameters which the user validates are the Application Requests headers like content type, Encoding, Response time, Authorization, and the Response which is fetched after hitting an API.
Input Parameter
Input parameters are passed important information that is necessary for an API to function and generate a response accordingly. In REST API parameters are passed through Query or Key value pair, Request body. 
Create positive and negative test case
Positive test cases
They are designed to check the basic functionality using the required parameters. Let's consider the previous example in which we validated user registration through an API. If we want to cover the positive scenario, we can create a list of all the valid parameters used in the 'First Name' field in real applications. For instance, it should accept alphabetic and numeric values, but it should not accept only spaces, etc. If we test our API covering all the valid parameters then it will be less vulnerable while designing a UI. 
Negative test scenarios
Negative test cases are designed to check how the API responds to prohibited operations using valid and invalid user input parameters like in the case of the previous example if we try to create a duplicate user or we are trying to create a user with a null value.
API Testing is like creating a strong foundation since without a strong foundation it is difficult to create anything of value. By prioritizing API testing and implementing strong security measures, you can establish a solid foundation for your application's development and protect it from potential vulnerabilities.
A secure API ecosystem gives overall system security and enhances user trust. Take action now! Share this blog post with your development, testing, and security teams to raise awareness about the importance of strong APIs and effective API testing.