Top API Security Best Practices You Need to Know

API security is the protection of the endpoints used to exchange data between applications, services, databases and third-party platforms. It includes authentication, authorization, data exposure, input handling, resource consumption and API configuration.

The OWASP API Security Top 10 is a popular reference to learn about API specific threats. This guide is aimed at practical API security best practices and how to design, develop, review, and build safer APIs.

Xcentric offers a variety of customized API development, REST/GraphQL services, third-party integration, secure key/token management, testing, and application maintenance services, all publicized openly.

A secure API is more than just an endpoint with a login screen. Security should be maintained from the moment the request is received until it is finally sent back, authenticated, validated, authorized, processed, accessed to the database, the response is generated, and it is logged and monitored.

The architecture of a new SaaS product, mobile app, customer portal, or integrated business platform can have security options that will be much simpler to manage than security controls put in place after deployment.

It's here that you'll benefit from API development expertise. Xcentric Services is not just about API architecture but also a part of the entire product, working on custom APIs RESTful and GraphQL integrations, web applications, SaaS solutions and connected business systems.

The OWASP API Security Top 10: An Overview

The OWASP API Security Top 10 is an API-specific security reference that is maintained by OWASP. The 2023 edition is the official API Security project presented by OWASP. The categories cover authorization failures, authentication, consumption of resources, sensitive business flows, SSRF, configuration, API inventory and unsafe consumption of external APIs. This is the current list:

The following is a very abbreviated overview. This is not an attempt to present a comprehensive catalogue of vulnerabilities; it is intended to give orientation before applying API security best practices. The project, according to OWASP's description, is a resource for developers, architects, managers, and security professionals who build, deploy, design, and manage APIs.

API Authentication Best Practices

Authentication is verifying who or what is requesting the API. Authorization, on the other hand, defines what the authenticated identity can do. If these are treated as a single control, there may be gaps in which a valid user successfully logs in, but does not get access that they deserve.

The first step to good api authentication practice is to choose the correct authentication method for the application, client, nature of the data, and trust relationship.

For many modern applications, OAuth 2.0 and correctly designed token-based authentication might be suitable. API keys can also be used to access services from one another, but do not be complacent about their use as harmless identifiers; they should be used as credentials.

Do not put credentials in the URL, as it could be in logs or in the browser history, monitoring, or infrastructure. Sensitive data should also not be hard-coded in a client-side application that a user can view.

Monitoring should be implemented in addition to authentication. If you log in successfully, it doesn't mean that all future requests are legitimate. If there are unusual authentication behaviors, repeated failures, use of a previously issued token, or unexpected geographical and/or behavioral patterns, it's worth further investigation.

Authorization: Object-Level and Function-Level Access Control

Authentication is asking the question 'Who are you?' Authorization is the question of "What can you access or do? This is an essential aspect of API security.

Object-level authorization determines if a user can access a particular resource. For instance, if the user is logged in to an account, he or she should not be able to get the invoice of another user by changing an identifier in the request.

Function-level authorization is for operations based on sensitivity. Normal customers can be successfully authenticated but should not have access to admin endpoints. A secure authorization model thus validates a permission for the specific operation and resource requested on the server.

Don't just use hidden buttons, front-end routes, or client-side checks. A user can make a request without going through a graphical interface, but instead going through an API. Authorization needs to be checked at the point where the protected resource or operation is actually used.

API Rate Limiting Security and Resource Protection

While authentication and authorization are critical to security, rate limiting is essential to api rate limiting security, as an API can be misused even if it is authenticated and authorized properly. There is a possibility of a legitimate client sending too many requests. Unusual traffic can be created with a compromised account.

An automated system can repeatedly make costly calls to endpoints. An attacker can cause intentional use of the resources of the application. Rate limits and quotas confine that consumption.

Rate limiting should be based on the real use of the endpoint. A read operation might have a different password reset limit or report generation endpoint.

Thus, API security is related to the multi-tenant systems' "noisy-neighbour" problem, which arises when one customer's heavy use of resources impacts another customer when resources are shared. Resource quotas and workload controls can minimize that risk. If you want to learn about multi-tenant SaaS architecture in general, check out our guide to it.

Rate limiting is not just a measure to fend off attackers. It can also contribute to availability, infrastructure capacity, and costs of operation.

Secure API Design: Integrate Security into the Architecture

Good API design begins before ever coding an API endpoint. The developers should decide what is exposed by each endpoint, who can call it, what data it needs, what it can change, and what might happen if it is called repeatedly.

It is helpful to have a deny-by-default approach: people should be able to access something only if they make an explicit decision to allow it. If validation is required, it must be performed and done so on the server, as validation can be circumvented on the client machine. API responses must also only give the information the client actually needs.

For instance, an endpoint that returns a customer's order status shouldn't return internal database fields, administrative flags, internal identifiers, or unrelated account information.

Error handling should be dealt with as well. Extensive debugging information is useful for developers while developing but should not contain secrets, database information, internal paths, stack traces, or other implementation information for external callers.

APIs communicating with other systems should also be considered when it comes to security. It should not be assumed that because the response is from another service, it is trustworthy. API architecture must take into consideration data flow, failure handling, permissions, authentication, and the systems involved on both sides of the integration for businesses creating complex integrations.

REST API Security Best Practices

The underlying principles of security are all the same for REST APIs as they are for other APIs, but there are some points to note. The most fundamental one is securing API traffic via HTTPS and TLS. Data such as sensitive credentials, tokens, and application data should not be sent across an unencrypted connection.

The HTTP methods need to indicate the action they are supposed to perform as well. Applications should not have any endpoints that are designed to return something by default but in fact are destructive.

Another practical consideration is versioning. If the API changes, the previous versions need to be monitored and phased out following a structured program. If no one is aware that an undocumented endpoint is accessible to the public, it can pose a security risk. Here are a few solid guidelines for rest api security from which to start:

REST security is thus not an independent field of study from API security. It's the actual implementation of the general principle of security on RESTful services.

Common API Vulnerabilities to Watch For

Knowing about potential API vulnerabilities facilitates teams in determining where to focus API implementation and architecture reviews. Authorization failures are important to note, as an API might be able to detect a user correctly but either allow that user to access the wrong object or function or allow the wrong user to access the correct function or object. Data exposure can be a problem when the endpoint returns a full representation of a database object instead of only the fields that the client needs.

When operations are expensive but have no clear limits, resource-consumption problems can arise. The configuration weaknesses could reveal debug functionality, permissive settings, outdated endpoints, and unnecessary services. An additional important question is API inventory. There may be an incomplete picture of the attack surface due to development, staging, legacy, and undocumented endpoints.

The bottom line is that API security is not a one-size-fits-all. The security of authentication, authorization, validation, resource protection, configuration, inventory, monitoring, and third-party integration must go together.

The Era of Agentic AI: API Security's Next Frontline of Defense

Agentic and automated systems can alter the real risk of current API vulnerabilities, as they can connect to APIs continuously and at machine speeds. For instance, a hole in the authorization that may require the human attacker to make many manual requests to investigate can be exploited much faster by an automated system. Likewise, when software can repeatedly call an endpoint without the slowdowns that would occur for human interaction, weak rate limits become a bigger issue.

When requests are systematically generated, hidden endpoints or endpoints that are not well documented may also become easier to enumerate. This is where API inventory and deny-by-default authorization become all the more essential.

The focus here is that this part is about classic vulnerabilities being used by increasingly automated activity. It is not about threats that are specific to the agent, like prompt injection or using the tool incorrectly. These areas are now the responsibility of security work by OWASP. The OWASP Top 10 for Agentic Applications 2026 is an independent one dedicated to autonomous and agentic AI systems, and the OWASP MCP Top 10 is dedicated to the security of Model Context Protocol servers and is in beta.

If the application uses AI capabilities to access tenant data, persist state, invoke external tools and/or run code through APIs, its architecture should be discussed accordingly instead of the application having only traditional API controls.

API Security Checklist

Lists of general principles are not useful. A helpful api security checklist would be something a developer, technical lead, or security reviewer could actually check. While thinking about an API that you want to use, consider the following questions about its security:

This checklist should be utilized during API development's life cycle, not just before launching. Security assumptions are often outdated as new endpoints are introduced, authentication protocols change, third-party integrations are added, or applications move into a new environment.

If your organization wants to create or review an API, instead of just reading about security, this is where development-as-a-service from specialists might be of benefit.

Building a More Secure API With Xcentric Services

Security is a critical factor in SaaS development, mobile apps, customer portals, internal systems, and API-driven workflows. Xcentrics' API development and integration services help create and implement custom API solutions for applications that require seamless integration with third-party platforms, databases, and business processes. It's a development offering with RESTful API, GraphQL API, API Integrations, Custom Application Development, and Backend Architecture.

The agency's overall development process encompasses architecture and development, integration, testing, launch and support, placing security in the overall product lifecycle and not at the end.

If the API is already in place, the first step could be an architecture and security audit: identify endpoints, audit authentication and authorization, review resource controls, audit data exposure, and review out-of-date and undocumented endpoints. In the case of a new API, one can start the discussion much earlier with the requirements, data understanding, data access, endpoint design, integration needs, and the right technology stack

For custom API development and integration, or to have an existing API reviewed, you can check out Xcentric's custom API services or discuss the requirements with its development team.