How can you verify data validation in web app APIs?

API input validation is a critical component of your design. You need to ensure your API handles both the happy path and negative scenarios. While you want to respond with appropriate error code and messages , you also must be protective about giving out too many internal details of your API in an error message. This could give more clue to a malicious actor.

I highly recommend starting with automated tests to get reasonable good test coverage, some of the ways to get started are PostMan Test Scripts if you are on the Quality check team. If you are on the DEV team who is developing REST API then execute automated tests as part of CI pipeline and leverage Microsoft.AspNetCore.Mvc.Testing and Microsoft.AspNetCore.TestHost as part of Integration test project.

Error validation is a great way to also enhance data input and output validation. You want to be sure that your application does not give away critical data when it encounters errors that are unhandled like code snippets, server fingerprint, snippets from db tables, etc. I have tested APIs that spit out internal code snippets when it encounters an unhandled exception. Fuzzing is a great technique to validate that the data input and output validation works as expected for most edge cases. This same technique is applied by hackers and malicious actors when testing apps so why shouldn't you?

Use JavaScript to implement client-side input validation so that common errors are detected before data is transferred to the server. As a result, the user experience is improved and the server load is lessened.

Data validation is not an isolated step in API development. Rather it is a continuous, iterative process, that works along side feature development. Data validation, logic validation, and other forms of testing are all part of the API development process.

You can skip input validation when there is no input required from users but you always need output validation to ensure proper communication. Not only, you need to avoid/filter any erroneous data in response but also keep the format intact. Changing the output format should be maintained with proper versioning.

In the symphony of web app APIs, output validation conducts a harmonious tune, ensuring that the melodies played by the server reach the client's ears without a discordant note. Postman, SoapUI, or Curl emerge as virtuoso conductors, orchestrating requests that echo across the API landscape. The resonating data, compared with expected output, becomes a melodious confirmation of accuracy and consistency. With tools like JSON Schema or XML Schema as sheet music, the API ensures that every response adheres to the predefined composition, creating a harmonious user experience.

I'd also emphasize the importance of not only validating the data format but also ensuring its integrity. I do regularly update and review JSON or XML schemas to ensure they align with evolving data structure and maintain long-term compatibility.

In my experience, evaluating the code's cyclomatic complexity has been instrumental in understanding the various use cases embedded within it. This metric gauges the code's complexity by counting the number of linearly independent paths through the program. By analyzing this complexity, I've been able to identify all the potential paths and outcomes that the business logic could encounter. This comprehensive understanding has allowed me to craft a testing strategy that achieves full coverage of the business logic for data validation. Tools like Postman became invaluable for systematically testing each scenario to ensure the API adheres to the defined business rules and behaves as expected across all use cases.

Always perform validation on the server side, even if you have client-side validation. Client-side validation can be bypassed, so server-side validation is essential for security. Check for the length, format, and type of data being sent. For example, if an API expects an integer, ensure that the received data is indeed an integer.

Well, requirements are placed using business logic and converted to technical spec thoroughly. Not only this, also after every phase of development it should be validated with current business logic. The expected relation between input & output must always agree with this.

In the dance of web app APIs, business logic validation choreographs the graceful movements of data, ensuring that each step aligns with the intricate ballet of the web app's functionality. Postman, SoapUI, or Curl takes on the role of skilled choreographers, directing requests that perform various business scenarios. The API's response becomes a performance review, indicating whether it flawlessly executes the expected actions and calculations, or if the dance requires refinement. A seamlessly choreographed API guarantees a web app ballet that mesmerizes users.

In addition to utilizing testing tools, I recommend implementing comprehensive unit tests and integration tests within the development process. Adopting a test-driven development (TDD) approach ensures that business logic is thoroughly validated from the outset. Incorporate dependency injection and mock objects to isolate components for testing, facilitating more granular assessments of specific business rules.

Well, it is the most sensitive part of almost all the projects & most of the exploiter mostly wanna gain access to this. To secure it we need to understand and group data, by their characteristics & requirements. i.e. lets look into some: - The server credentials should be maintained within .env file(s). - To communicate among data storing servers, should use latest secure auth techniques - Sanitize data before sending in data server - If sensitive data must be stored, then make sure data is properly encrypted with secure algorithms - Unless data (which is sensitive, like password) need to be retrieved hash it with proper salting using latest, reliable, most hard (or currently impossible) hashing algorithms .... & so on.

Amid the digital arena of web app APIs, data security validation stands as a vigilant sentinel, safeguarding the fortress of sensitive information. Postman, SoapUI, or Curl, armed with authentication methods like tokens or certificates, scrutinize every request. The response becomes a beacon, signaling if the API enforces the required security measures. In this digital citadel, unauthorized access is thwarted, and data integrity prevails, ensuring compliance with the stringent policies and regulations governing the web app.

Data integrity, consistency and freshness is important. - Every data should be type casted to reflect proper data type. - Quality differs from project to project, never compare one with another. Otherwise you will face bottlenecks or over processing.

In the narrative of web app APIs, data quality validation weaves a tale of completeness, accuracy, and relevance. Postman, SoapUI, or Curl, akin to diligent storytellers, send varied requests, querying, updating, or deleting data. The response data, examined against the database tapestry, narrates the saga of data integrity, consistency, and freshness. A compelling narrative spun by the API ensures a web app that captivates users with its usability, reliability, and efficiency.

Within the dynamic rhythm of web app APIs, data performance validation takes center stage, ensuring that every beat resonates with speed, scalability, and resilience. JMeter, LoadRunner, or Gatling emerge as maestros, orchestrating requests that test the limits of load, concurrency, and frequency. The API's response time, throughput, and error rate become the crescendo, signaling whether it harmonizes with performance requirements and SLAs. In this symphony of speed and stability, the API becomes an enduring masterpiece, captivating users with its optimized performance.

Within the vast expanse of considerations, let's reflect on the essence of these validations. It's not just about the mechanics of testing; it's about orchestrating a symphony of secure, accurate, and performant APIs. In this space, we acknowledge that the heart of web app excellence lies in the meticulous validations that fortify the system, creating an immersive user experience and ensuring the digital ballet unfolds flawlessly.

If you're working on a project that has a public APIs, you might want to think about using GraphQL. It's like giving your API's users a 'choose your own adventure' book. Instead of you guessing what data they need, they tell you exactly what they want each time. This makes everyone's life easier - you don't have to make a bunch of different versions of your API, and your users get just the data they're looking for, nothing more, nothing less