API Security: A Technical Guide

In the rapidly changing field of software development, application programming interfaces (APIs) are very powerful tools. They allow different applications to communicate, share data, and collaborate seamlessly, constituting approximately 71% of all web traffic.

However, as APIs become more essential to our applications, they also attract cyber threats. In fact, 57% of organizations reported experiencing at least one API-related data breach in the past two years. As such, a failure in API security can lead to data breaches, service interruptions, and harm to your reputation—along with potential legal and financial consequences.

But what is API security? It is a simple fact that you need to protect your APIs from unauthorized users and harmful actions. This may require measures, e.g., proper user verification and access controls, as well as monitoring API traffic for abnormal activities.

This guide will closely examine the security of APIs- and their importance, address common threats, and give practical advice on protecting your APIs. 

What is API Security?

API security is the practice of protecting APIs from unauthorized access, misuse, and vulnerabilities to ensure the confidentiality, integrity, and availability of data and services by implementing authentication, authorization, rate limiting, input validation, and encryption. 

By addressing both design flaws and runtime risks, it safeguards critical systems from threats such as data breaches, injection attacks, and DDoS. Without it, your application becomes an open door for attackers to exploit.

Why API Security Matters?

API security remains a top priority for organizations, including small businesses and large enterprises. Security risks such as broken authentication, authorization, and data disclosure complement the growing dependence on APIs, and as they do, they endanger the digital infrastructures of your organization. 

Challenges for CXOs

For CXOs, API breaches can lead to significant financial losses, reputational damage, and legal repercussions, making the security of APIs a critical concern at the executive level. 

Such issues around C-level concerns make it the responsibility of CXOs to create robust API Security programs across your organization that combine authentication, strong authorization, encryption, and monitoring.

Challenges for Security Engineers

Security engineers face an ever-evolving landscape of cyber-attacks targeting APIs, requiring continuous adaptation and proactive defense strategies. Engineers need ongoing education and remember the OWASP Top 10 threats against APIs and other prevailing attacks.

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Recommended Reading: 10 Best API Security Testing Companies To Consider in 2025

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Challenges for Businesses

Businesses increasingly rely on APIs, which introduces new security challenges affecting operations and customer trust.  As the dependency on APIs increases, so do the associated security challenges, such as broken authentication, authorization, and data disclosure. 

Understanding these challenges and implementing effective security measures is essential for protecting digital infrastructure and maintaining trust with customers and partners.

Types of API & Their Security

There is always a concern regarding the security of APIs as it impacts the application’s quality and overall reliability. GraphQL, Rest, SOAP, and gRPC all have different security issues. In this section, we will discuss various security issues associated with these types of APIs.

GraphQL 

API’s representational state transfer has a new layer, graph QL, which enables the clients to ask for the exact data they require. Due to its nature, there are certain security shortcomings GraphQL has:

• Authorization and Authentication: Normally, a GraphQL endpoint’s singular request is able to handle multiple queries and mutations, which puts it at risk of poor Authentication and Authorization. Therefore, strong mechanisms are necessary to ensure the access restriction is enforced.
• Querying Complexity: GraphQL has the capacity to have multilayer nested queries, which increases the risk of performance issues, including DoS attacks and systems shutting down; hence, these issues can be handled through query complexity assessment and limits placed on them.
• Input Validation: Like most APIs, injection attacks can be avoided as long as the input validation and sanitization are done in the correct manner, which GraphQL queries should be able to do by modifying their schema constraints for validation purposes.

REST 

Representational state transfer, or REST, is a popular architectural style that is used in the creation of applications on the web. Some of the important aspects regarding the security of the REST APIs include:

• Authentication Mechanisms: Apply security standards such as OAuth 2.0, JWT (JSON Web Tokens), or API keys to the API so that only the approved persons can access the API.
• HTTPS: There is always the need to ensure that every API endpoint is using HTTPS because it helps protect data that is in transit from being intercepted.
• Rate Limiting and Throttling: Rate limiting and throttling add a layer of security to an API by reducing the number of requests a client can make, preventing overwhelming volumes of requests, and aiding in preventing the exposure of services to Denial of Service attacks.

SOAP

The simple object access protocol is a message protocol that is used when passing structured information in web services. Some of the important aspects of SOAP API security include the following:

• WS-Security: The use of WS-Security within SOAP APIs enhances the security that exists at the message level. Such type of security includes addressing confidentiality, integrity, and availability of messages.
• XML Encryption and Signatures: SOAP messages are encrypted and signed, thus preventing tampering and unauthorized access.

gRPC

gRPC is a high-performance, open-source framework for remote procedure calls (RPCs). Security considerations for gRPC APIs include:

• Transport Security: gRPC is performed over HTTP/2. HTTP/2 can be secured using TLS (Transport Layer Security), which encrypts the data in transit.
• Authentication: gRPC uses multiple forms of authentication, including token-based, SSL/TLS certificate-based, and OAuth 2.0.
• Authorization: Defining fine-grain authorization methods would help to ensure that only legitimate clients have access to certain services or methods.

The Three Pillars of API Security

APIs are everywhere, powering the apps and services we use daily. But with great connectivity comes great responsibility. Following are the three core pillars that keep APIs secure.

API Observability

API observability is the foundation of a secure and optimized API infrastructure. Its in-depth analytics into APIs’ behavior, performance, and usage allows you to discover and resolve problems proactively before they become critical. 

Ongoing API traffic, usage patterns, and monitoring performance metrics ensure that APIs run optimally and securely. Such an approach enables high availability, low downtime, and a better user experience overall.

Key Components of API Observability

• Logs: A verbose record of all API requests and responses that may help with troubleshooting and user activity tracking.
• Metrics: Quantifiable data regarding API performance (response times, error rates, throughput, etc.).
• Traces: Traces provide end-to-end tracking of API requests, making it easier to identify bottlenecks and understand how data flows through the system.

API Vulnerability Scanning

Scanning for API vulnerabilities on an ongoing basis is crucial to detect and remediate security risks. Frequent scanning is needed to ensure vulnerabilities are acted on before a new threat to APIs arises. Such proactive steps are extremely important for keeping the APIs secure and unbreached.

Types of Vulnerabilities to Scan For:

• Broken Authentication: Issues with authentication mechanisms that can lead to unauthorized access.
• Injection Attacks: Vulnerabilities that allow attackers to inject malicious code into API requests.
• Security Misconfigurations: Incorrectly configured security settings that can expose APIs to attacks.
• Excessive Data Exposure: APIs that expose more data than necessary, potentially leading to data breaches.

To effectively scan for vulnerabilities, several tools can be used by companies:

• OWASP ZAP (Zed Attack Proxy): An open-source tool that helps find security vulnerabilities in web applications, including APIs.
• Burp Suite: A comprehensive platform for testing API security, offering free and premium versions with advanced features.
• Astra Security: A security tool that provides automated vulnerability scanning for APIs and web applications.

API Protection

API protection solutions need to have some ongoing protective mechanisms for attacks that happen in real-time. These mechanisms are classified into two parts.

Preventative protection is when you implement mitigations to stop attacks before they occur. You can do this with regular vulnerability scans and secure coding guidelines. In contrast, you can work towards reactive protection, simply detecting and responding to real-time attacks, e.g., using intrusion detection systems, incident response plans, etc.

Some of these include:

• Rate Limiting and Throttling: Limits the number of requests that can be made from a client in a given period to protect from abuse and DoS attacks.
• IP Whitelisting/Blacklisting: Limiting the API access using the IP address to control who can be exposed to the API.
• Web Application Firewalls (WAFs): Utilization of WAFs to filter and monitor HTTP requests coming into and out of an API, blocking requests posing a threat.

Common API Security Challenges

APIs have become one of the most important connections between applications. Unfortunately, these APIs are not easy to secure. Organizations struggle with multiple challenges that put the integrity and security of the APIs at risk. Let’s take a look at some of the common security challenges.

Authentication and Authorization

One of the most fundamental aspects of API security is ensuring that only authorized users and applications can access the API. Authentication is the process of verifying who the user is, while authorization is the process of verifying what the user can do. 

Nevertheless, weak passwords, insecure token storage, and missing MFA allow threat actors to gain entry. Security issues such as excessive users with admin access or misconfigured RBAC can lead to users gaining access to resources they do not have access to, making the situation even more complicated.

API Observability

API observability helps you understand and track the information regarding the API behavior. But getting complete observability is hard with zombie and shadow APIs. Zombie APIs are APIs that are out of service but still open for queries, representing significant security risks in case they are left without visibility. 

Shadow APIs, however, are created and deployed without the knowledge of IT or security teams, are poorly secured, and can be used for malicious purposes by threat actors.

Data Exposure and Leakage Risks

APIs often handle sensitive data, and exposure or leakage can have severe consequences. Excessive data exposure, where APIs return more data than necessary, can inadvertently expose sensitive information. 

Also, improperly stored data can be easily accessed by attackers, leading to data breaches and other security incidents. Ensuring data is securely transmitted and stored is essential for maintaining the integrity of APIs.

Injection Attacks (SQL, Command Injection, XSS, etc.)

Injection attacks are a common and dangerous threat to APIs. These attacks involve injecting malicious code into API requests to manipulate the system. Types of injection attacks include SQL injection, where attackers inject SQL code to manipulate databases.

Command injection, where attackers inject commands to execute arbitrary code on the server, and cross-site scripting (XSS), where attackers inject scripts to execute in the user’s browser. These attacks can compromise the security and integrity of APIs, leading to data breaches and other malicious activities.

Session Hijacking and Replay Attacks

Session hijacking occurs when an attacker gains unauthorized access to a user’s session, allowing them to impersonate the user and perform actions on their behalf. Replay attacks, on the other hand, involve capturing and replaying API requests to impersonate a user. 

Insecure session management practices, such as weak session tokens and improper storage, make it easier for attackers to hijack sessions.

Insufficient Monitoring and Logging

Effective monitoring and logging are essential for detecting and responding to security incidents. However, many organizations struggle with implementing comprehensive monitoring and logging practices. 

Incomplete logs and the lack of real-time monitoring can make identifying and investigating security incidents difficult, allowing them to go undetected for extended periods. This insufficiency in monitoring and logging can leave you vulnerable to attacks and unable to respond effectively to security threats.

Best Practices for API Security

Ensuring the security of APIs is vital for protecting sensitive data and maintaining the integrity of applications. Here are some best practices for API security testing that organizations should consider implementing:

Strong Authentication (OAuth, OpenID Connect – OIDC)

Implementing strong authentication mechanisms is one of the most important aspects of security for APIs. OAuth 2.0 and OpenID Connect (OIDC) are widely used standards for securely managing user access to APIs. OAuth 2.0 provides a secure framework for authorization, allowing clients to access resources on behalf of users without exposing their credentials.

OpenID Connect extends OAuth 2.0 (OIDC) by adding an identity layer, enabling users to authenticate themselves and obtain an ID token that can be used to verify their identity. These protocols use JSON Web Tokens (JWTs) to securely transmit authentication and authorization information securely, ensuring only authorized users can access API endpoints.

const passport = require('passport');

const OAuth2Strategy = require('passport-oauth2');

passport.use(new OAuth2Strategy({

    authorizationURL: 'https://authorization-server.com/auth',

    tokenURL: 'https://authorization-server.com/token',

    clientID: 'xxxx',

    clientSecret: 'xxxx',

    callbackURL: "http://localhost:3000/auth/callback"

  },

  function(accessToken, refreshToken, profile, cb) {

    // Verify user and handle token storage

    return cb(null, profile);

  }

));

// Protect routes with authentication

app.get('/api/users,

  passport.authenticate('oauth2', { session: false }),

  function(req, res) {

    res.json({ message: "Hello from Astra!!" });

  }

);

API Gateway and Rate Limiting

Using an API gateway can help manage and secure API traffic. API gateways are a single entry point for all API requests, providing a centralized location for enforcing/implementing security policies. 

One of the key features of API gateways is rate limiting, which helps prevent abuse and denial-of-service (DoS) attacks by limiting the number of requests a client can make within a specific timeframe. 

Rate limiting can be implemented at various levels, such as per user, per IP address, or API key, ensuring that APIs remain available and performant. API gateways can also handle other security measures such as authentication, authorization, and traffic encryption, making them an essential part of a secure API architecture.

const rateLimit = require('express-rate-limit');

const apiLimiter = rateLimit({

  windowMs: 15 * 60 * 1000, // 15 minutes

  max: 100, // Limit each IP to 100 requests per windowMs

  message: {

    error: 'Too many requests, please try again later.'

  }

});

app.use('/api/', apiLimiter);

Encrypting API Communication (SSL/TLS)

Encrypting API communication using SSL/TLS is essential for protecting data in transit. SSL/TLS provides a secure channel between the client and the server, ensuring the data exchanged is encrypted and cannot be intercepted or tampered with. This is achieved through digital certificates, which establish a secure handshake between the client and the server.

SSL/TLS ensures data integrity by using message authentication codes (MACs) to verify that the data has not been altered during transmission. Implementing SSL/TLS for all API communications is a fundamental security measure that helps prevent eavesdropping, man-in-the-middle (MiTM) attacks, and data breaches.

Input Validation and Sanitization

Input validation and sanitization help prevent injection attacks, such as SQL injection, command injection, and cross-site scripting (XSS). Validating and sanitizing all user inputs can help ensure that only the API processes safe and well-formed data. This involves checking input data against predefined rules and constraints, such as data types, lengths, and allowed characters (using whitelisting/blacklisting characters).

For example, parameterized queries and prepared statements can prevent SQL injection by separating the SQL code from the user input. Similarly, sanitizing user inputs to remove potentially harmful characters such as “<” or “>” can prevent XSS attacks.

const { body, validationResult } = require('express-validator');

app.post('/api/user',

  body('username').trim().isLength({ min: 3 }).escape(),

  body('email').isEmail().normalizeEmail(),

  body('password').isLength({ min: 8 }),

  async (req, res) => {

    // check for validation errors

    const errors = validationResult(req);

    if (!errors.isEmpty()) {

      return res.status(400).json({ errors: errors.array() });

    }

    const { username, email, password } = req.body;

    // using parameterized queries

    const query = 'INSERT INTO users (username, email, password) VALUES (?, ?, ?)';

    try {

      await db.query(query, [username, email, password]);

      res.status(201).json({ message: 'User created successfully' });

    } catch (error) {

      res.status(500).json({ error: 'Database error' });

    }

  }

);

Zero Trust Principles for APIs

Implementing zero-trust principles for APIs involves assuming that all traffic is potentially malicious and verifying every request. This approach includes strict authentication and authorization mechanisms, as well as continuous monitoring and verification of API traffic.

Zero trust principles require that every API request is authenticated and authorized, regardless of its origin. This can be achieved through multi-factor authentication (MFA), least-privilege access controls, and micro-segmentation. Continuous monitoring and dynamic access controls can help detect and respond to suspicious activities in real time.

Implementing Logging and Monitoring

Logging and monitoring are essential for detecting and responding to security incidents. Comprehensive logging practices should capture all relevant API activity, including requests, responses, user actions, and system events.

Logs should be stored securely and retained for a sufficient period to do forensics in case of a security incident. Real-time monitoring tools can help detect and respond to security incidents promptly. These tools should be configured to alert security teams to anomalous activities, such as unusual traffic patterns, failed authentication attempts, and unauthorized access.

const winston = require('winston');

const expressWinston = require('express-winston');

const { ElasticsearchTransport } = require('winston-elasticsearch');

// Configure Winston logger

const logger = winston.createLogger({

  level: 'info',

  format: winston.format.combine(

    winston.format.timestamp(),

    winston.format.json()

  ),

  transports: [

    // Console logging for development

    new winston.transports.Console(),

    // File logging for production

    new winston.transports.File({ 

      filename: 'error.log', 

      level: 'error',

      maxsize: 5242880, // 5MB

      maxFiles: 5,

    }),

    // Elasticsearch transport for centralized logging

    new ElasticsearchTransport({

      level: 'info',

      clientOpts: { node: 'http://localhost:9200' }, // replace with production ES URL

      indexPrefix: 'api-logs'

    })

  ]

});

Regular Security Assessments

Conducting regular security assessments can help identify and address vulnerabilities in APIs. Security assessments should include vulnerability scanning, penetration testing, and code reviews. Vulnerability scanning tools can automatically detect common security issues, such as injection vulnerabilities, cross-site scripting (XSS), and broken authentication mechanisms.

Penetration testing involves simulating real-world attacks to identify vulnerabilities in the API’s security posture. Code reviews should be performed to ensure that best practices are followed and that there are no hardcoded credentials, weak encryption algorithms, or other security flaws.

API Versioning and Deprecation Policies

Implementing API versioning and deprecation policies helps manage the lifecycle of APIs. Versioning allows for backward compatibility and smooth transitions between API versions. Each version of the API should be documented, and changes should be communicated to developers to ensure that they can update their applications accordingly.

Deprecation policies ensure that outdated and potentially insecure APIs are phased out. This includes setting a deprecation timeline, notifying users, and providing alternatives or migration paths.

Documentation and API Inventory Management

Maintaining comprehensive documentation and an up-to-date API inventory helps manage and secure APIs. Documentation should include details on API endpoints, authentication mechanisms, usage guidelines, rate limits, and error handling.

Clear and concise documentation helps developers understand how to use the API securely and efficiently. An API inventory helps track all APIs, ensuring they are properly managed and secured. This includes identifying and decommissioning unused or zombie APIs, which can pose security risks if left unmonitored.

Incident Response Planning

Having an incident response plan can help with effectively handling security incidents. The plan should include procedures for detecting, responding to, and recovering from security breaches. This includes defining roles and responsibilities, establishing communication protocols, and outlining steps for containment, eradication, and post-incident analysis.

The incident response plan should be regularly tested and updated to ensure effectiveness. Additionally, you should have a well-documented process for reporting security incidents to relevant stakeholders, including customers, partners, and regulatory authorities.

Final Thoughts

In an era where APIs are the lifeblood of modern applications, prioritizing API security is not just a best practice but an imperative. Failure to do so can lead to devastating consequences, including data breaches, financial losses, and reputational damage.

By understanding the core pillars of security for APIs – observability, protection, and vulnerability scanning – and implementing the best practices outlined in this guide, you can significantly enhance the security posture of their APIs.

Remember, API security is an ongoing journey, not a one-time event. As the threat landscape evolves, so too must your security measures. You can build a robust and resilient security strategy by staying informed, adopting a proactive approach, and leveraging the latest tools and techniques.

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