Back to Glossary

API Key

API keys are fundamental building blocks of modern software development that enable secure communication between applications and services. These unique identifiers authenticate and authorize applications accessing an API, providing a straightforward way to control access to resources, monitor usage, and maintain security. Understanding API keys is important for developers who need to integrate external services or protect their own APIs.

API keys serve multiple purposes: they are used to authenticate requests, track usage metrics, and enforce rate limits. While they offer simplicity and ease of implementation, API keys also require careful management to prevent security vulnerabilities. This guide explores how API keys work, their benefits and limitations, and best practices for implementation.

What is an API key

An API key is a unique identifier that serves as a means to authenticate and authorize applications accessing an Application Programming Interface (API). It functions as a secret code that allows API providers to verify the identity of requesting parties and ensure interactions are legitimate and permissible.

API keys are usually long, alphanumeric strings generated by API providers and distributed to developers of applications requiring access. When making an API request, applications include the API key in a request header or as a body parameter. This inclusion allows the API to authenticate the request and authorize access to specified resources.

Here's an example of an API key in a HTTP request:

GET /v1/resource HTTP/1.1
Host: api.example.com
Authorization: Bearer YOUR_API_KEY_HERE

What are API keys used for

API keys are used to facilitate secure authentication and access control. Key use cases include:

  • Authentication: Since each API key is unique and secret, it can be used to verify which application is making a request.
  • Usage monitoring: API keys are used to track the number of requests made by each application. This data assists in usage analysis, billing, and identifying trends or potential abuse.
  • Authorization and access control: API keys can restrict or grant access to specific parts of an API, and ensure applications can only read or write resources if they have permission.
  • Rate limiting: API providers can implement rate limits based on API keys. This prevents a single application from overwhelming the service with too many requests in a short time.

Evolution of API keys

The history of API keys parallels the development of web services and distributed computing. As software systems became more interconnected, the need for secure access to remote services emerged.

The late 1990s and early 2000s saw the rise of web APIs, and API keys emerged as an elegant solution for managing and securing access to web services. Companies like Salesforce, eBay, and Amazon pioneered the use of API keys to manage access to their services, establishing them as a standard security mechanism.

Modern API keys support sophisticated features like rate limiting, access restrictions, and usage tracking. While they remain widely used, the evolution of security requirements has led to complementary authentication methods like JSON Web Tokens (JWT) and OAuth 2.0, offering enhanced security features for more complex scenarios.

How do API keys work

API keys operate through a straightforward process of generation, distribution, and validation. The workflow follows these steps:

  1. Generation: API providers create unique keys using secure random number generators.
  2. Distribution: Keys are securely shared with authorized developers or applications.
  3. Implementation: Developers include keys in API requests through headers or parameters.
  4. Validation: API servers verify keys and process requests based on associated permissions.

Security best practices

To maximize API key security:

  • Store keys securely using environment variables or secret management tools.
  • Implement HTTPS to prevent key interception.
  • Use rate limiting to prevent abuse.
  • Rotate keys frequently.
  • Monitor key usage for suspicious activity.
  • Implement additional security layers for sensitive operations.
  • Keep keys out of version control and public repositories.

Secret API keys vs publishable API keys

Some services offer both secret and publishable API keys. In these cases, secret keys are for backend environments and must be kept confidential. They enable direct access to sensitive operations.On the other hand, publishable keys are used in public contexts for untrusted operations, like collecting user input.

Typically, actions that use a publishable key are used in tandem with a secret key. For example, in the case of collecting a payment, a an API request requiring the secret key will be used to specify the purchase amount, while an API request requiring the public key will used to collect the user's credit card information. This ensures that the user is not trusted to set the payment amount.

API keys in Clerk

Clerk's authentication service implements a dual-key system using publishable and secret keys.

Publishable keys (prefixed with pk_test_ or pk_live_) handle client-side operations and are expected to be exposed in frontend environments. Secret keys (prefixed with sk_test_ or sk_live_) manage sensitive server-side operations and must remain confidential.

Developers typically store API keys as environment variables, which are supported across most development and production environments.

In the Next.js development environment, applications use the pair of API keys labeled with test, and store them in the .env.local file. In the Vercel production environment, applications use the API keys labeled with live and store them as Vercel Environment Variables.

The API keys can be retrieved from Clerk's dashboard on the API keys page.

Related terms