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How to Take Over Fintech with APIs: Development, Optimization & Integration Tips

APIs are everything in the Fintech world. To reign in the data-driven age, you need to gather and process tons of information, and APIs claw and drag it relentlessly. Unseen, they are the core power underneath the lion's share of Fintech processes: “open” in “open banking” stands for “open APIs.”

Explore with me the intricacies of developing, optimizing, and integrating APIs. I'll guide you through the most popular API protocols, ways to optimize API development and integration, and steps to best secure APIs.

What API protocols to use

First things first. Let’s take a look at the most actively used protocols for building APIs and see when to use each.


REST is perhaps the most popular architecture. 

  • It is stateless, which means every request should provide the app with all the information needed to fulfill it. Unlike with other APIs, the servers of RESTful ones won’t remember previous requests, even if they’re similar.
  • Data output types supported include JSON, CSV, and HTTP. 
  • You can secure REST with Secure Sockets Layer/Transport Layer Security (SSL/TLS).
  • Use REST for web development projects: it's unparalleled in providing access to web services. Mind that you should implement robust security for data exchanges, clients, and deployment.
  • RESTful APIs are a good fit for public use, but you can also base your internal APIs on REST architecture.
  • Such APIs can communicate directly over HTTPS using the language of their choice or operate through middleware such as BitPay, or load balancer.


The first API architecture ever, Remote Procedure Call (RPC) is a simple means to send multiple parameters and receive the desired result. 

  • While RESTful APIs merely exchange data or resources, RPC is a remote executable action of process or processes. 
  • RPC can employ two formats: JSON and XML.


While SOAP is not as popular today as REST and RPC, it’s a sure match if your primary concerns are standardization and security. 

  • SOAP supports SSL/TLS and  Web Services Security and has built-in error handling.
  • It can require complex implementation and app refactoring due to exposing application logic components as services rather than data.
  • SOAP can employ XML and HTTP.


Released by Google in 2016, this protocol has already gained its share of popularity as the evolved design of RPC.

  • GRPC achieves higher performance in microservices. 
  • It supports the first and second HTTP versions (the latter incorporates the features of the first one, which makes it more powerful). However, the second GRPC version is yet to see its popularity, perhaps, because it’s not so well documented compared to other standards. I decided to review it a couple of years ago, and it took me much time.Top Protocols for Building APIs

How to develop APIs quickly (and save the quality)

Two approaches can help you with that. Both are centered around an API contract — the documentation that explains your API to its consumers. Based on that, there are two approaches — code-first and contract-first.


With this approach, first comes the discussion — how the API will look like, what endpoints it will have, and what data you receive upon this or that request. Thus you form a contract, and after that, the back-end team and the client’s team start the development simultaneously. 


  • If there’s enough time allocated for the discussion and the contract is well-detailed, then the time for the development can shrink significantly, even more than with the code-first approach. 

Thus this approach fits best large enterprises that might want to launch another product and have all the time they need.

  • However, if you’re a small startup, a thorough discussion will help you forge a robust basis of documentation. That’s especially beneficial for startups or the company that is creating PoC. 
    Contract-first or code-first


Basically, it’s the “just do it” approach. 

You have a front-end team, a back-end team, and an application. The teams work separately on a web application, an Android client, and an iOS client. First, your back-end team codes all the functionality and then passes it to the front-end team to create a fully-fledged API. In this case, before the development, no one knows how the finalized API will look eventually. 


  • “Minimal effort contract” - teams won’t generate the contract until the very end. Thus back-enders create a lightened code: API is built with the code alone, and there are no expectations set in the form of a contract.

 A warning here: with the contract-first approach, you might have a gap between the contract and the realization if the team lacks ideas or if something else goes wrong during the discussion.

  • If you need to develop a public API, this approach suits you better, simply because there’s no contract required in this case - you create the rules.

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Security recommendations for building an API

Whether you have API as a product or API as the part of your application, they both provide access to sensitive data or network resources, so you have to protect them. 

Below, I list eight tips for completing that multi-step security quest.

#1 Authenticate and authorize

OAuth 2.0, OpenID Connect, and JSON web tokens can help you authenticate API traffic and control access to API resources.

#2 Enable and test controls

If you have third parties tapping your internal data and systems through APIs, you should control who can access what and when. Also, your teams need to check every change to the data, be it adding new data, deleting, or editing some.

#3 Encrypt API communication 

APIs often exchange sensitive data via requests and responses, so using HTTPS to protect it is a must. It’s better to go for HTTP Strict Transport Security to avoid unexpected behavior of API clients.

#4 Validate the data 

Cleaning and validating data on your company’s side should be obligatory — better to be safe with zero trust than sorry with standard injection flaws and cross-site request forgery attacks. Debugging tools can help you streamline the process.

#5 Minimize the amount of data you share

Ensure that API filters the information and the responses include only relevant parts.

#6 Make security tests regular

To ensure APIs are functioning and behaving as they should, you’ll need your security teams to check their security controls regularly. If there’s evidence of an API threat, your incident response teams must be ready with a clear action plan to address the issue.

#7 Carefully manage your API keys

When possible, keep the keys out of the API code or app’s source tree files, place them in environment variables or secret management tools, periodically change the keys and delete the ones you no longer need.

#8 Power up API monitoring and threat detection with AI

AI can help identify suspicious behavior patterns by providing insights into how users interact with APIs. 

API Security Checklist

How to optimize your API performance 

  • Review all the code, particularly the responses, and groom the amount of information you’re asking for to reduce the time for the response.
  • Enable API caching to find frequently accessed data quickly.
  • Use the PATCH method for partial updates, which is much quicker than PUT. 
  • Prevent abuse.
  • Limit payloads.
  • Use API webhooks: they allow you to send a request just once, setting a trigger to receive the response when the desired event occurs rather than keep calling until the server can give you the relevant data.

Tips for smooth and secure API integration

  • Give the documentation a thorough review to make the best out of the API
  • Integrate only well-tested APIs from reputable providers.
  • Double-check APIs’ security and maintenance.
  • Make sure the API is scalable so that it keeps up with your business expansion.
  • Use API SDKs; it’s an API packaged with all the development tools and documentation to simplify the API use and integration. When DocuSign and Stripe released SDKs for their APIs, they made the lives of thousands of developers much easier.

Not sure what's the best way for your business to go about APIs?
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The final lines

By following the tips I included above, you can develop a business tool that enables secure and powerful data exchange for you and your clients. But what matters most is who will create, optimize, and integrate this tool.

A team responsible for such a critical part of your Fintech offering should act as one and have a strong background in the industry. I am lucky to be part of such a team that supports many successful projects

Schedule a quick call for a free consultation and see how we can help your business grow.




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