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Custom API development: the devil’s in the details

API software development

Make sure to develop a secure custom API if you don’t want to let the intruders in.

No software today can run in isolation. Even the simplest programs integrate with third-party services to complement their functionality and provide customers with an enhanced user experience. Such software collaboration is beneficial for both the receiving and the sending sides. The former easily uses off-the-shelf third-party services, while the latter grows in popularity and strengthens brand awareness.

If you want to let other apps use the services of your product, you need to develop a custom API. It will act as a gate that lets other services in while keeping your app secure and protected. 

In this article, we will explore  API development,  what integration approaches to use, and what pitfalls you may face.


An API (Application Programming Interface) is a set of functions that allows you to connect to program services and integrate them into your software. API developers create special algorithms that define program responses to particular actions. In the API documentation, they describe:

  • available operations

  • input data

  • output data.

APIs can be implemented for external and internal users. Depending on the development purpose, APIs are divided into three types: private, partner, and publiс.

A private API is used by company staff. It is developed for internal purposes to unite all corporate apps into single enterprise software.

A partner API is developed for business partners. It is used in joint projects to enhance the functionality of involved apps.

A public API is open for all those who wish to use it. The developers can utilize a public API if they want to enable third-party services in their software.


A custom  API is not a standalone product, but an add-on that integrates with existing software. So, the question of creating such a product is often controversial, being incorrectly influenced by the opinions of other organizations. At Erbis, we’ve worked with many custom API development projects, and here are the top 5 misleading views we’ve faced.

1. An API has nothing to do with business. Many owners consider API software development a purely technical need. Nevertheless, it is a great business opportunity to promote your product through third-party services and reach a more extensive consumer base.

2. An internal API is not needed. While organizations realize the value of open APIs, they may underestimate APIs designed for internal needs. However, by refusing private API development, companies reduce the chances of building efficient enterprise software and establishing smooth business processes.

3. Many public APIs are a sign of company success. In fact, a large number of open APIs can lead to customer churn and reduced brand awareness. This is because third-party apps often use secondary features of your app while diverting from the core functionality of your software.

4. A public API can survive without marketing efforts. Building an API for public usage is expected to bring benefits to an organization. However, why would anyone want to connect to your weather forecast service, for example, in preference to your competitor who offers the same functionality? If you aim to monetize your product, you should create a unique value proposition and spread the word about your offerings.

5. A public API must be paid. Many companies see a custom API as an extra source of income. Yet, a straightforward monetization, such as pay X dollars and connect, may be ineffective. A more practical solution is providing customers with free API usage and growing the customer base by delivering unique services and tools.


The choice of architectural approach affects the practicability of using an API. For example, monolithic components are not entirely autonomous. Instead, they are loosely interconnected by a specific service. The changes in such a service entail changes in each dependent app component. Microservice architecture, by contrast, sets complete module autonomy, and a change in one of them does not affect any of the others at all. 

Microservice architecture is more advanced because it allows easy editing of specific modules without redoing the whole app structure. The communication between microservice modules goes through an API, often  REST (Representational State Transfer) API –  while in monolithic architecture the communication is through ESB (Enterprise Service Bus). 

In ESB solutions, all services pass through a single place and have a single point of failure. On the contrary, in microservice apps, the units are independent, each designed to perform a single business task. In addition, REST API, commonly used in microservices, allows fast processing and light message format. This enables prompt communication between the app modules with minimum overhead and low network latency.

Thus, if you start a new project, we recommend choosing a microservice architecture. It helps to quickly develop and deploy an app and easily scale it up as the business grows. Besides, a well-designed API layer enables smooth communication between the app modules and ensures a glitchless software operation.


An API is a way to communicate with third-party services; that is why developers should pay special attention to API security. When we talk about common pitfalls in API development, we, first of all, mean security gaps that may affect software functionality and lead to data leakage. 


Many online systems use APIs to transfer private user data, including medical and financial information. Lack of authentication leads to data breaches and ruins a company’s reputation. To avoid this, developers should use proven authentication setup methods when creating an API. The most common methods are API key, basic authentication, cookie-based authentication, and token-based authentication. In addition, developers must adhere to generally accepted API standards for authentication and authorization, such as OAuth 2.0, OpenID Connect, and WebAuthn.


Some developers allow API authentication with any token value different from null. This approach is extremely unprofessional and provides easy data access for intruders. All they have to do is put a non-zero token value into the authorization request, and the system will accept it as correct. Developers should always provide a token value for security matters regardless of whether the API is public, partner, or private.


Weakly encrypted data becomes an easy target for attackers. To avoid unauthorized access, developers must enable strong encryption during data transmission and storage. It is necessary to implement SSL (secure socket layer) and TLS (transport layer security) for secure data transmission. As for secure data storage, the best practice is to apply AES (Advanced Encryption Standard) or DES (Data Encryption Standard).


Some APIs do not limit the number of requests and may be flooded with traffic coming from external services. As a result, the server gets overloaded, leading to decreased software performance or a complete crash. This situation results from DDoS (Distributed Denial of Service) attacks that aim to destroy the system with the endless flow of requests to the software server. To prevent this, API developers should implement configurable traffic and speed limits to restrict input data and reduce system overload risk.


The lack of authorization causes another security hole in API development. There is an opinion that strong authentication is enough for the reliable protection of a web-based API, but it is not so. Authenticated but unauthorized users can access someone else’s data by simply changing the user ID. Furthermore, if the IDs are numbered sequentially, the hacker’s task becomes even easier. All they need to do is add numbers one by one to get access to different customers’ data.


Modern software solutions connect with various applications and process data streams from different sources. Application Programming Interface makes this interaction fast and smooth, allowing one party to integrate third-party services and the other to share them securely.

Whether you want to connect to external resources or let them connect to your software, you need to hire API developers who have extensive experience with API development tools and understand what tech stack to choose for a given project.

Today any API of web services is implemented through REST or SOAP (Simple Object Access) protocols. SOAP API supports XML format, whilst REST API supports XML, JSON, and many other formats (in other words it is not format-dependent).

If you want to develop a custom API so that other solutions can connect with your services, SOAP vs. REST choice will depend on many factors. For example, REST is better suited for stateless operations – and SOAP  for continued operations. If you want to integrate third-party services into your app, you must create a client-side that connects with the necessary source through a REST or SOAP API. In this case, users of your application do not choose which protocol they should use for message sending, but they have some elegant solution to use and they are familiar with it: usually, it is some library that may be included in another application and used by it programmatically.

Custom API solutions also include cloud API integration. Such APIs are essentially no different from other application interfaces and allow you to connect to cloud providers such as AWS or Microsoft Azure and use their services to develop, deploy, and support your product.


A high-quality and secure API makes your product an attractive resource for third-party solutions and helps grow your customer base. Also, a custom API allows you to quickly integrate with partner applications or build an efficient software system for enterprise needs.

To develop a custom API, you need to choose the right technology stack: data transfer protocols, authentication and authorization methods, encryption tools, etc. If, on the other hand, you want to enable external services in your product, you need to integrate with the third-party API using appropriate development approaches and API connection techniques.  For non-tech people, this task is rather challenging. Also, it might not be wise to hire an in-house team because API development projects usually do not last longer than 5-6 months. So, if you need to implement a custom API quickly and efficiently, consider outsourcing this task to a specialized team with deep expertise and a perfect reputation in software development. 

September 22, 2021