5 Best Practices for Securing Your API Gateway

October 30, 2023

API gateways are the front door to all your microservices. The API gateway’s central role in routing makes it both a valuable tool for simplifying microservices-based applications and a critical point for security.

They are responsible for safeguarding the application from external threats, ensuring that only legitimate requests are processed and that malicious or malformed data doesn’t compromise the underlying services. Therefore, correctly setting up security protocols and policies in an API gateway is paramount. Any oversight can lead to potential vulnerabilities, making the entire microservices ecosystem susceptible to breaches or disruptions.

The overarching concept to think about is zero trust. Any user, request, origin or action has to be validated and authenticated before being granted access. In a zero trust model, trust is never implicit; it must always be earned and continuously verified, ensuring that every interaction with the API gateway is secure and legitimate.

Here are five best practices for implementing zero trust in your API gateway within five core security concepts.

Authentication: Use Token-Based Authentication with Short-lived Tokens

Authentication is a foundational security aspect in API gateways. As the primary interface between external entities and internal services, an API gateway’s ability to accurately and securely authenticate requests is critical to the system’s overall security.

At the authentication process’s core is ensuring that the entity making the request is who it claims to be. You can use API keys to authenticate your API gateway, but token-based systems like OAuth 2.0, allow for granular permissions, enabling specific actions or resource accesses based on the token’s claims.

Token-based authentication, especially when using stateless tokens like JSON Web Tokens (JWTs), doesn’t require the server to keep a session state, making it suitable for large-scale, distributed applications. Tokens can also be signed and encrypted, guaranteeing data integrity and confidentiality. JWTs, for example, allow claims to be embedded directly into the token, which the server can validate.

You minimize the potential damage of token leaks or theft by keeping the token’s lifespan short and using refresh tokens when necessary. Token-based authentication is also widely adopted and understood, making integrations with third-party services or systems easier.

That said, it’s essential to understand that even the best practice, if implemented poorly, can lead to vulnerabilities. Proper key management, secure token transmission (such as using HTTPS), validating token signatures and guarding against token reuse are all crucial aspects of this best practice.

Authorization: Strictly Enforce Role-Based Access Control (RBAC) for All API Endpoints

The gateway’s role in authorization is to act as an intermediary that checks each request against a set of permissions before allowing it to proceed. API gateways frequently serve multiple applications, user roles and services. This diversity of interaction means that not every authenticated entity should have access to all resources. For example, a user authenticated as a regular employee might not have the same data access rights as someone authenticated as an administrator.

As such, API gateways should use the principle of least privilege. You never want a user, internal or external, to have more access than they absolutely need. Enforcing RBAC for all API endpoints ensures that every user or service is granted only the permissions necessary for their specific role or task. This minimizes the risk of unauthorized access or actions, bolstering the overall security of the API gateway and the microservices it protects.

If a user or service credential is compromised, RBAC ensures that the attacker can only access limited resources, minimizing potential damage. By granting permissions strictly based on roles, you inherently provide only the minimum necessary access, encapsulating the essence of the principle of least privilege.

By adopting a rigorous RBAC approach, an API gateway upholds these tenets, ensuring that every user or service interacts only with the resources they genuinely need, thus enhancing overall system security.

Rate Limiting: Implement Dynamic, Layered Rate Limiting Based on User Behavior and Context

Rate limiting is often seen as a means to ensure system availability and prevent service degradation during normal use. But from a security perspective, rate limiting acts as a first line of defense against various malicious activities, such as distributed denial of service (DDoS) attacks. By capping the number of requests from a particular source or to a specific endpoint, an API gateway can effectively prevent a flood of requests from overwhelming the backend infrastructure, thereby ensuring continued service availability to legitimate users.

The problem is finding the right balance between legitimate requests and malicious actors. Instead of using a one-size-fits-all rate limit, take a dynamic approach that allows you to adapt limits based on user or client behavior. Thus, a user with typical behavior might be allowed more requests than a user showing signs of suspicious activity.

You can do this by using a layered approach to rate limits. Instead of relying on a single rate limit, use a combination of different rate limits, such as:

  • IP-based limits: Restrict the number of requests from a specific IP address.
  • User ID or token-based limits: Differentiate between authenticated users.
  • Endpoint-specific limits: Deploy rate limits for critical or potentially exploitable endpoints.
  • Contextual: Evaluate the context of the request. For instance, API requests that modify data (such as POST, PUT, DELETE) could have a different rate limit than read-only requests (GET).

With this approach, genuine users will receive the best service quality, while potential attackers will find it challenging to perform brute-force, scraping or DDoS attacks. However, be careful that rate limiting doesn’t inadvertently block legitimate traffic or create a denial-of-service scenario for genuine users. Proper monitoring and alerting mechanisms should accompany rate limiting to address any such issues promptly.

CORS: Explicitly Define and Restrict Allowed Origins

When a browser-based application tries to access an API not in its origin, the browser first sends a preflight request using the HTTP OPTIONS method. This is asking the API (through the gateway) for permission to perform the request. The API gateway’s responsibility is to respond to this preflight request with the appropriate CORS (cross-origin resource sharing) headers, informing the browser about the allowed origins, methods and headers.

From a security standpoint, the implications are significant. An overly permissive CORS policy, such as allowing any origin to access the API, can expose sensitive data or operations to malicious sites. Bad actors could use this for data theft or even trigger unwanted side effects in the context of a user’s session.

This is why you need to always avoid wildcards. Using a wildcard (*) to allow any origin to access resources is risky and should be avoided.

Instead, specify exactly which origins (domains) are permitted to access the API. If you have a specific frontend service that is communicating with your backend through an API gateway, this is simple in the API gateway configuration file:


Restrict access to only trusted origins. It will minimize exposure and significantly reduce the risk of unwanted cross-origin requests and potential data breaches.

By diligently specifying allowed origins and resisting the temptation to use broad wildcards, the API gateway can successfully balance accessibility and security, keeping malicious cross-origin interactions at bay.

Logging: Implement Real-Time Monitoring and Alerting for Anomalies

Logging in API gateways is about capturing relevant information related to the requests and responses flowing through the gateway. This often includes details like:

  • Timestamps: Provide a chronological record, allowing teams to track the exact time an interaction occurred, which is vital for debugging and incident analysis.
  • Source IP addresses: Identify a request’s origin to help track user behavior, troubleshoot issues and detect potentially malicious activity.
  • Endpoints accessed: Gauge usage patterns, optimize resources and detect unauthorized access attempts by noting which API endpoints are accessed
  • Response times: Monitor how long it takes for an API to respond helps assess performance, ensure timely data delivery and identify potential bottlenecks.
  • Status codes: See the result of the request, whether it’s successful, produces an error or results in a server issue, aiding in diagnostics and service quality monitoring.
  • Headers: Access vital metadata about a request or response, like content type or authentication tokens, which are essential for processing and security validations.
  • Payloads: Capture the main content of a request or response as it can be crucial for debugging application issues or understanding the data exchange context.
  • Query parameters: Log this information as it helps you determine response content, understand user queries and ensure the correct data is returned.

Effective monitoring can identify potential system bottlenecks, service degradations or malicious activities. For instance, a sudden spike in failed login attempts or requests from a particular IP range could indicate a brute-force attack or potential API abuse. Established predefined thresholds or patterns of interest (repeated failed login attempts, unexpected HTTP methods or unusual traffic spikes) can act as the trigger for alerting response teams about potential security concerns.

Logging and monitoring in API gateways also play a crucial role in post-incident investigations. In the event of a security breach or service outage, logs serve as a primary source of truth, helping teams trace back events leading up to the incident, identifying root causes and planning mitigation strategies.

Zero Trust Is Better for Your Legitimate Users

A secure API gateway means a better experience for your trusted users.

When unauthorized and malicious requests are effectively filtered out, the system’s resources are better allocated toward serving genuine users, ensuring faster response times, consistent uptime and a more reliable user experience. Furthermore, with the heightened security measures of a zero trust approach, users can confidently interact with the platform, knowing their data is safeguarded against potential breaches.

Adding the above options to your API gateway can be as easy as adding another line to your YAML file. With modern API gateways, enhancing security often doesn’t require extensive overhauls, just a simple configuration change. This ease of implementation means there’s no excuse for neglecting robust security practices.

Article originally published on thenewstack.io

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