APIs facilitate communication between different software applications and power a wide range of everyday digital experiences, from weather apps to streaming services and everything in between. They are also a critical ingredient of AI. However, if not structured and standardized properly, APIs can become inconsistent, insecure, and difficult to maintain. This is where API specifications come into play.
An API specification is a blueprint that outlines the expected structure of API requests and responses, authentication mechanisms, error-handling procedures, and other crucial details. Enforcing API specifications ensures that APIs are consistent, secure, maintainable, and interoperable. In this blog, we’ll explore API specifications in more detail, including why, when, and how to enforce them.
What is an API Specification?
Put simply, an API specification defines how different software components communicate with one another. It provides a structured guideline for developers and systems to follow when implementing and interacting with APIs, including:
- Endpoint Definitions: The URL paths clients use to interact with the API.
- Request Methods: HTTP methods such as GET, POST, PUT, and DELETE.
- Request and Response Formats: Defines the expected data formats, such as JSON or XML.
- Authentication and Authorization: Specifies security protocols such as OAuth, API keys, or JWT tokens.
- Error Handling Mechanisms: Standardized error responses and status codes to ensure predictable behavior.
The OpenAPI Specification (previously known as the Swagger Specification) is arguably the best-known and most widely adopted specification. It defines an API’s structure and capabilities in a way that is both human and machine-readable, meaning developers can use it for validation, testing, and automation.
Here’s an example of an Open API Specification document used to define and describe a REST API:
1 openapi: 3.0.0
2 info:
3 title: Sample API
4 description: Optional multiline or single-line description in [CommonMark](http://commonmark.org/help/) or HTML.
5 version: 0.1.9
6
7 servers:
8 - url: http://api.example.com/v1
9 description: Optional server description, e.g. Main (production) server
10 - url: http://staging-api.example.com
11 description: Optional server description, e.g. Internal staging server for testing
12
13 paths:
14 /users:
15 get:
16 summary: Returns a list of users.
17 description: Optional extended description in CommonMark or HTML.
18 responses:
19 "200": # status code
20 description: A JSON array of user names
21 content:
22 application/json:
23 schema:
24 type: array
25 items:
26 type: string
How Does it Differ from an API Definition?
Although the terms “API specification” and “API definition” are often used interchangeably, it’s important to understand that, although fundamentally linked, they have distinct meanings.
API specifications describe what an API does, focusing on its functionality and design; API definitions describe how an API works, providing a machine-readable, technical blueprint. Specifications are for understanding and design, while definitions are for implementation and automation.
Think of an API like a house. The specification is the architectural blueprint, while the definition is the detailed construction plan. As such, definitions are typically derived from specifications.
Why Enforce API Specifications?
Now that we have a better understanding of what API specifications are, we can look a little deeper at why they’re important. Enforcing API specifications is crucial because they provide:
- Consistency: A well-defined API specification ensures that all developers follow the same guidelines, leading to uniformity in how services communicate. This consistency simplifies integration and reduces the likelihood of errors.
- Security: Enforcing API specifications helps implement standardized security measures like authentication and authorization protocols. This reduces vulnerabilities and protects against potential threats.
- Maintainability: Clear specifications make updating or modifying services more manageable, as developers can understand the expected behavior and structure of the API.
- Interoperability: Standardized APIs allow different systems and applications to work together seamlessly, facilitating integration and collaboration across platforms.
Moreover, to enforce API specifications is to operate on a positive security model. This means that only requests explicitly defined and permitted within the API specification are allowed. Conversely, a negative security model operates on a “default allow” approach, blocking only known malicious patterns. Here’s a breakdown of each model’s respective strengths and weaknesses:
| Positive Security Model | Negative Security Model | |
| Security Level | Generally higher security as only known safe actions are permitted. | Lower security as new threats may not be blocked until discovered. |
| Maintenance | Requires frequent updates to allow new safe actions. | Requires frequent updates to block new threats. |
| Complexity | More complex to implement and manage due to the need to define all allowed actions. | Simpler to set up initially but can become complex with growing threat lists. |
| False Positives | Higher risk—may block legitimate activities if not explicitly allowed. | Lower risk—legitimate actions are generally allowed unless mistakenly blocked. |
| False Negatives | Lower risk—only explicitly allowed actions can occur. | Higher risk—new or unknown threats may bypass detection. |
When Should You Enforce API Specifications?
Developers should enforce API specifications throughout the development and deployment process. There are three key moments at which enforcement is essential. They are:
During Development
Enforcing API specifications from the very beginning of the development process ensures that developers build all components of the API correctly and consistently. Developers should use linting tools to check for inconsistencies, code reviews to ensure adherence, and mock servers to test API interactions before implementation.
Before Deployment
Developers must also validate APIs against specifications before releasing them into a production environment; this ensures there aren’t any inconsistencies or security risks. To validate APIs against specification, developers should:
- Running compliance tests to verify that API endpoints match the specification
- Using API gateways to enforce policies and monitor traffic
- Ensuring proper documentation is available for API consumers
When Integrating Third-Party Services
Organizations often rely on third-party APIs to extend functionality or integrate external services. When consuming third-party APIs, it is essential to verify that they comply with required security and data-handling standards. This can prevent potential security risks and ensure smooth integration with existing systems.
During Production
It’s especially important to enforce API specifications during production to validate live traffic, prevent attacks, and detect anomalies. You must continuously monitor for shadow APIs, log events, and implement version control. Moreover, real-time alerts and rate limiting ensure security and stability.
Best Practices for Enforcing API Specification
Okay, so we’ve covered the why and the when, but we still haven’t got the all-important how. Failing to follow best practices when enforcing API specifications can create security vulnerabilities, functional issues, and operational issues – so here’s our advice.
Use Schema Validation
Wallarm’s API Firewall functions by employing schema validation. It uses API specification to create a blueprint of expected communication. As traffic flows through the firewall, it meticulously compares each request and response against this schema. The firewall then flags any deviation from the defined schema.
Based on its configuration, the firewall will either log these discrepancies or actively block the non-compliant traffic. In the case of REST APIs operating in logging mode, the firewall extends its validation to discover ‘shadow’ APIs, which are functional endpoints not explicitly documented in the specification, logging their presence alongside the validation failures.
Implement Automated Testing
Automated testing tools can help detect non-compliant API implementations early in the development process. Some possible testing approaches include:
- Contract testing to validate that APIs meet predefined specifications
- Schema validation to check request/response formats
- Security testing to identify vulnerabilities and enforce compliance
Wallarm’s API Security platform automates API testing with auto-generated and/or user-provided OpenAPI specifications.
Maintain Comprehensive Documentation
Maintaining API documentation ensures that developers understand and follow the defined specifications. Well-documented APIs improve the developer experience and reduce implementation errors. Wallarm’s API Discovery module automatically maps and updates API inventories based on real traffic, ensuring accurate and up-to-date documentation. This reduces manual effort and enhances visibility.
Monitor API Traffic for Compliance
Organizations should continuously monitor API traffic to detect any deviations from the expected specification. Wallarm provides real-time API monitoring, detecting unauthorized access, malicious payloads, and performance issues. What’s more, our AI-driven anomaly detection prevents attacks, ensures data integrity, and even optimizes API performance.
How Wallarm Can Help
Wallarm’s API Specification Enforcement secures your APIs by validating requests against your defined specifications. It detects discrepancies – such as undefined endpoints, invalid parameters, or missing authentication – between the specification and actual API traffic. When inconsistencies occur, Wallarm automatically takes preconfigured actions: blocking, logging, or ignoring the request based on risk.
This positive security model significantly simplifies API protection. It means you avoid creating and constantly updating restrictive rules and eliminate the risk of missing attacks due to unconfigured rules. What’s more, we automate the entire process to reduce administrative overhead and misconfiguration risks. And, just when you thought it couldn’t get any better, we minimize resource consumption by setting limits on processing time (50ms) and request size (1024KB). Here’s an overview of how the whole process works:
Want to learn more about Wallarm’s approach to API specification enforcement? Check out this resource.
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