Implementing API Key Authentication in ASP.NET Core

APIs often use API keys to authenticate clients and authorize access to endpoints. In this post, we'll look at different approaches to implement API key authentication in ASP.NET Core.

What are API Keys?

API keys are unique identifiers that a client sends to the API in requests to identify itself and authenticate. They are an alternative to token-based authentication like OAuth. Compared to tokens, API keys:

• Are simpler to implement and use
• Transmit identification but not details about the client
• Stateless so don't expire and no refresh needed
• Allow basic level of security

API keys are commonly used to:

• Identify API consumers
• Rate limit requests
• Revoke individual client access
• Analyze API usage

ASP.NET Core API Key Authentication

There are few different ways API keys can be implemented in ASP.NET Core:

1. As a Query Parameter

API keys can be sent in the query string for each request:

To authenticate:

2. As a Header

API keys can also be sent as a custom HTTP request header:

Read and validate the header in code:

3. With an Authentication Middleware

For more advanced authentication, create a middleware to validate the API key on each request:

This keeps the key validation logic in a single place and preserves separation of concerns.

4. Using Policies and Authorization

For role-based access, the API key can be used to determine a user's roles and authorization:

This scales authorization beyond just identification, allowing for richer access control rules.

Final Words

Implementing API key authentication allows securing an ASP.NET Core API simply and flexibly. Keys can identify consumers and authorize access if used alongside policies. Just be sure to store and transmit the keys securely. With robust API key implementation, you can protect access to valuable API resources and functionality.

Read More: .NET Core Libraries for Programmers