Guide To Secure API Development

March 18, 2024

In an age powered by data and innovation, safeguarding APIs—the backbone of modern applications—is crucial. These open interfaces facilitate seamless system integration and help organizations tap into their data’s potential. Unfortunately, their very accessibility also makes them prime targets for threats.

API security vulnerabilities can lead to breaches of sensitive user data, business logic manipulation, and denial-of-service attacks, posing severe threats to organizations. Recent research indicates that only 40% of organizational APIs undergo consistent vulnerability testing, with many attacks going inadequately addressed. This underscores the critical importance of integrating API security throughout the software development lifecycle (SDLC).

This article offers a comprehensive roadmap to building APIs while ensuring that security is baked in from the start to the end of the SDLC. When you’re done, you’ll clearly understand best practices and actionable tips for holistic API security.

Summary of key secure API development concepts

Development Phase Description
Requirements and Planning Collect and analyze requirements for the software, including security needs. Validate these requirements against business objectives. Conduct a risk assessment to prioritize security concerns.
Design and Architecture Create architecture and design documents, incorporating security aspects like encryption, authentication, and data protection mechanisms. Perform threat modeling.
Development Develop the software based on the design while adhering to coding standards and guidelines emphasizing security.
Testing Run multiple tests, including functional, performance, and, most importantly, security tests (e.g., vulnerability scanning and penetration testing).
Deployment Release the software into the production environment. This should include steps to configure the background and monitor for security incidents securely.
Maintenance and Monitoring Continuously monitor the application for security incidents. Patch and update the software as needed to address new threats and vulnerabilities.

The secure API development life cycle

Building secure APIs requires integrating security practices into each phase of the development process. The diagram below shows an overview of key activities across the secure API development life cycle.

OWASP - Secure Development and Integration (source)

#1 Requirements and planning

Secure APIs start with gathering security requirements alongside functional needs. Planning for security from the start is crucial: It’s far easier and more cost-effective to build secure APIs from the ground up than to attempt to retrofit security measures later.

The role of security in requirements gathering

The following steps ensure security while defining the functional requirements in the beginning stages of API development:

  • Define your API security goals: Start by identifying the key security objectives for your APIs and align these goals with your organization’s broader security priorities and risk appetite. A few example objectives could be:
    • Preventing data breach or loss events
    • Guarding intellectual property and proprietary algorithms
    • Resisting real-world threats like fraud, DDoS attacks, etc.
  • Classify API sensitivity: Not all APIs require the same level of protection. Categorize APIs into sensitivity tiers based on data exposed and the potential impact of compromise, such as these:
    • High: APIs dealing with personally identifiable information (PII), financials, healthcare data, etc.
    • Moderate: APIs handling intellectual property, proprietary algorithms, or B2B data exchange
    • Low: APIs exposing non-sensitive data and functions
  • Map out compliance requirements: Identify relevant regulatory and industry standards, like HIPAA, PCI-DSS, and SOX, that prescribe security controls for your APIs and data flows. Build compliance into the design from the start.

#2 Design and architecture

The design phase focuses on defining robust API architectures, platform features, and infrastructure to provide defense in depth.

Threat modeling

Threat modeling involves identifying potential threats and vulnerabilities, prioritizing risks, and defining mitigations. It is a continuous process providing insights to strengthen the planned architecture and design.

The continuous process of threat modeling (source)

The STRIDE model—Spoofing, Tampering, Repudiation, Information Disclosure, Denial of Service, and Elevation of Privilege—is a commonly used framework for conducting threat modeling in API development.

Adopt a secure-by-design philosophy

The secure-by-design philosophy emphasizes security from the start of development rather than as an afterthought. This approach endorses principles like enabling security by default, adhering to the principle of least privilege, employing layered protections, isolating sensitive APIs, ensuring that APIs fail safely, and maintaining simplicity to avoid exploitable gaps.

Adopt a RESTful API architecture

what is rest API?
REST API (source)

RESTful API architecture is favored for its inherent security benefits compared to more complex SOAP-based architectures. Its fundamental constraints, such as statelessness, a client-server architecture, and a uniform interface with standardized HTTP verbs, all contribute to reducing vulnerabilities, enhancing performance, and facilitating the integration of security controls.

Tools like Impart can assist with generating documents and diagrams across the Software Development Lifecycle.

#3 Development

During development, APIs should be implemented while incorporating essential security controls directly in the code.

Secure authentication

Authentication ensures the identity of users, systems, or apps, safeguarding APIs from spoofing, tampering, and unauthorized disclosures. It’s best to use established protocols like OAuth 2.0, OpenID Connect, and JWT instead of custom methods. These standards facilitate the validation of scopes, state parameters, and specific OAuth flows while advocating cryptographic best practices such as using secure, random numbers for token generation.

Roles involved in an Oauth 2.0 and OpenID connect authentication flow for the Microsoft identity platform (source)

Use JWT libraries instead of custom JWT creation to prevent errors. Ensure token security with encryption, proper key management (explained later on), and secret rotation. Automate the revocation of compromised or expired tokens for safer authentication.

Enforce authorization

After successful authentication, it’s crucial to manage API resource access with authorization controls. Using role-based access control (RBAC) or attribute-based access control (ABAC) ensures tailored access permissions. By following the principle of least privilege and adopting row-level security and tenant isolation in multi-tenant apps, you can greatly reduce unauthorized access risks.


Validate all inputs

Rigorous input validation is crucial to thwart injection attacks. Effective strategies to ensure clean, correct, and valuable data operations include adopting OWASP recommendations. Examples of these are employing allowlists over denylists, constraining data types, sanitizing inputs, and revalidating on the server side (even if client-side validation has been executed).

The following code snippet shows a basic example of validating incoming data in Python using a library like Pydantic.

from pydantic import BaseModel, ValidationError

class RequestModel(BaseModel):
    name: str
    age: int

    RequestModel(name="John Doe", age="twenty")
except ValidationError as e:

The code in the try block will fail because the supplied data (age="twenty") fails the integer requirement in the Pydantic model.

Implement robust logging

Logging is indispensable for security monitoring, incident investigation, and forensics. Capture detailed authentication events, input validation failures, and API call specifics. Ensure that logs are tamper-proof, possibly through digital signatures or centralized storage, and mask sensitive fields to prevent exposure to confidential data.

Handle errors securely

Striking a balance in error handling to provide debugging context without exposing sensitive system details is vital. Employ generic error messages, classify error severity, obfuscate details, and log extensively internally for diagnostic purposes.

The following code snippet demonstrates how to craft informative yet non-leaky error messages in a Flask API.

def not_found(error):
    return jsonify({'error': 'Resource not found'}), 404

def internal_error(error):
    return jsonify({'error': 'Internal server error'}), 500

Enable rate limiting

Rate limiting is crucial to safeguard APIs against abuse, such as brute-force login attempts and DDoS attacks. User-level, server-level, and geography-based rate limiting can be employed using various rate-limiting algorithms such as the token bucket, leaky bucket, fixed window, and sliding window algorithms to efficiently control the rate of requests.

Implement secure caching

Enhance API performance and guard against traffic surges using secure caching. Use Cache-Control: private to stop intermediaries from storing resources. Carefully handle cache keys, particularly by adding secondary keys like Vary: Cookie. This segregates cached data based on different cookie values, preventing the unintentional sharing of sensitive details among users.

Encrypt sensitive data

Employ encryption meticulously for data in transit using HTTPS and TLS and for data at rest through database and file encryption. Utilize tokenization, masking, and data minimization strategies to further bolster sensitive information security.


Securely store secrets

Proper secret storage is critical to prevent unauthorized access. Avoid hard-coding secrets and opt for secure storage solutions like Hashicorp Vault. Implement robust key management practices, including systematic key rotation, deployment automation, and granting least privilege access to developers for essential tasks.

Follow secure coding standards

Adhere to secure coding standards by reusing trusted libraries, utilizing parameterized queries to prevent SQL injection, removing developer comments from code before production deployment, and enforcing strict typing and input-output filtering to detect and rectify issues early in the development cycle. Many IDE and stand-alone tools can assist in a shift-left approach with security linters during development, ensuring a secure API that avoids misconfigurations like those found in the OWASP API top 10.

#4 Testing

Robust security testing is pivotal to identifying vulnerabilities before they reach production. By integrating these testing mechanisms within the CI/CD pipeline, timely feedback can be achieved, promoting a more secure development lifecycle.

Static and dynamic application security testing (SAST and DAST)

SAST and DAST form the core of automated security analysis. SAST evaluates raw source code for vulnerabilities like memory leaks without executing programs, facilitating early issue detection at code check-in time. DAST proactively assesses running applications for flaws, such as injection attacks. Incorporating tools like OWASP ZAP and Impart can bolster static and dynamic analyses, seamlessly integrating them into the CI/CD pipeline and developer IDEs for a well-rounded security assessment and timely feedback throughout development and during builds.

Runtime application self-protection (RASP)

Stopping real-time attacks (source)

RASP focuses on safeguarding live APIs in the production environment by actively monitoring and neutralizing threats in real time, ensuring continued security post-deployment. Runtime protection can be employed using tools like Impart, which uses machine learning technology for real-time evaluations, ensuring a comprehensive framework that provides ongoing security assurance in the dynamic landscape of API threats.

Penetration testing

Utilize external penetration testers for live-fire exercises that emulate real-world attacks, mirroring likely adversaries. Scheduling periodic penetration tests on critical APIs and infrastructure throughout the year offers objective insights into exploitable gaps, aiding in promptly remedying identified vulnerabilities. This exercise is important to ensure the robustness of your API’s defenses against simulated threat attacks.

Fuzz testing

Fuzzing, a robust testing mechanism, sends unexpected or malicious data to APIs to observe behavior and uncover flaws. Attempting to crash systems or provoke unusual behaviors can flag potential vulnerabilities, contributing to mitigating unforeseen security risks that might be exploited in a real-world scenario.

#5 Deployment

The deployment phase encompasses setting up and managing infrastructure through infrastructure as code (IaC) tools such as Terraform and Ansible and securely launching APIs into production with a focus on scaling ongoing protections.

Utilizing API gateways

Utilize API gateways to route API traffic, standardizing security and enhancing performance. This enables DDoS protection via rate-limiting, reduces latency with caching, and ensures data security with authentication, authorization, and correct HTTPS/TLS configurations. Popular gateway options include Kong, Tyk, Apigee, Amazon API Gateway, and Azure API Management.

How Amazon API Gateway handles, processes, and routes API requests (source)

Protecting endpoints

Enhance public-facing API security by reducing exposed IPs and open ports and implementing a web application firewall (WAF) to screen traffic for threats. Block unnecessary HTTP methods, enforce up-to-date TLS and cipher suites, and maintain robust security.

Leveraging a secure CI/CD pipeline

Integrate DevSecOps in a secure CI/CD pipeline using automated tools to scan vulnerabilities in infrastructure, configurations, secrets, dependencies, and containers at every stage. Use DAST scans in build pipelines and implement IaC for consistent security baselines. Automation in these pipelines minimizes risks from manual configurations, ensuring continuous security with fewer human errors.

#6 Maintenance and monitoring

Monitoring and alerting

Real-time threat detection is enhanced by effective monitoring and logging. Monitor logins and token usage for irregularities, suggesting credential breaches or account takeovers. Track changes in roles, permissions, and groups. Monitor API traffic for odd patterns, durations, or IPs, indicating potential DDoS or brute force attempts. Analyzing metrics like response times or error rates can highlight potential denial-of-service threats. It is advisable to utilize tools like Impart to automate the monitoring and alerting of anomalies while blocking suspicious activity.

Payload inspection

Examining API payloads enhances security by revealing unknown vulnerabilities, policy breaches, and attack patterns. This involves detecting unusual API payloads, testing for injection attacks, and checking for sensitive or malicious data.

Effective payload inspection practices may encompass sampling live traffic, masking or tokenizing sensitive fields before logging, and leveraging AI techniques like anomaly detection to identify sensitive information in unstructured data flows.

API lifecycle and asset management

Optimally managing API lifecycles, including versioning and deprecation, is vital for security. Use tools to automatically identify APIs, keys, and data flows, ensuring constant inventory and preventing loss over time. Embracing API lifecycle platforms reduces security risks from outdated APIs and keys. Automated asset management further maintains a real-time view of all API assets.

Security retrospectives and continuous improvement

Regular cross-functional retrospectives on security incidents, penetration tests, and abuse scenarios are vital to suggest control enhancements. This ongoing evaluation aids in assessing the current security protocols and pinpointing areas to strengthen API security.



Securing APIs requires a coordinated effort encompassing people, processes, and technology. It starts with integrating security into the API design and continues throughout its lifecycle. Adopting a DevSecOps mindset is essential, and tools such as Impart simplify the process by automating key security tasks on a single cloud platform. By following the roadmap in this article, you’ll strengthen your APIs against evolving cyber threats and maximize the benefits of APIs for a secure digital transformation.

Contact Impart Security at for more API security tips and best practices and be sure to follow us on LinkedIn for the latest product news and updates.

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