Securing data and protecting user privacy are paramount concerns in web applications. As the backbone of modern web applications, Representational State Transfer (REST) APIs play a crucial role in facilitating communication between different services. However, the openness and accessibility of APIs make them susceptible to unauthorized access and data breaches. One of Google Cloud’s 2022 reports on API security insights and trends states that over 50% of organizations faced an API-related security threat at least once in 2021, confirming that APIs have become a favorite target for threat actors. Thus, you want to ensure you can trust the identity of each request made so that only authorized users gain access to the sensitive data or privileged operations. Enter authentication methods that act like gatekeepers and grant access to the APIs only for authorized users. This blog post will explore various REST API authentication methods, highlighting their strengths, weaknesses, and best practices.

What is REST API Authentication?

API authentication verifies a user’s identity to confirm they have the necessary permissions to access an API/API Data.

Specifically, authentication allows API owners to do three things:

1. Verify the identity of a client or user.
2. Enable authorized clients and users to access the API.
3. Prevent unauthorized access.

This is tightly linked and often needs clarification with another idea – authorization. Following authentication, authorization is how vendors govern which APIs users can access.

Authorization is used for:

1. Granting access and exposure to particular resources or data for different users.
2. Governing what actions different users and clients can take with our API.
3. Otherwise, enforce defined access control policies.

Hence, authentication verifies an identity, and authorization provides access to specific resources.

Here are the four ways to implement authentication in your REST API services:

Basic Authentication

Basic Authentication is a simple and widely used method for authenticating users in RESTful APIs. It involves sending a username and password with each request to the server, typically done through the HTTP headers. Despite its simplicity, it’s important to note that Basic Authentication is less secure than more advanced authentication methods, primarily when used without additional security measures like HTTPS; hence, it is not recommended for sensitive data or production environments.

Here’s a basic overview of how Basic Authentication works in REST API:

1. Request from the Client:

When a client (a web or mobile application) requests the server, the authentication information is included in the request headers.

2. Encoding Credentials:

The username and password are combined into a string in the format `username: password`. This string is then base64-encoded. It’s important to note that base64 encoding is not encryption; it’s just a way to represent binary data (the concatenated username and password) in ASCII format.

3. Including Credentials in Request Header:

The base64-encoded credentials are included in the HTTP request header. The header typically looks like this:

  Authorization: Basic base64(username:password)

  For example:

  Authorization: Basic QWxhZGRpbjpPcGVuU2VzYW1l

4. Server-Side Authentication:    

The server receives the request and extracts the Authorization header. It decodes the base64 string to obtain the original username and password. The server then validates these credentials against its authentication system.

5. Authentication Result:

 The server processes the request as usual if the credentials are valid. If the credentials are invalid, the server returns a 401 Unauthorized status code, indicating that the client needs to provide valid credentials.

It’s important to use HTTPS when implementing Basic Authentication to encrypt the communication between the client and the server. The credentials are sent in plain text without encryption, making it vulnerable to threats. 

API Keys

API keys are a simple and commonly used authentication method in RESTful APIs. An API key is a long alphanumeric string unique identifier for a client or application accessing an API. It is often sent as a parameter or included in the request headers. Here’s an overview of how API key authentication works in REST API:

1. Obtaining API Key: Developers or clients request an API key from the API provider. This is usually done through a developer portal or some registration process.
2. Including API Key in Requests: Once the API key is obtained, it must be included in each API request. 
   • There are different ways to include the API key:
     • In the URL: “https://api.example.com/resource?api_key=your_api_key”
     • In the Headers: Api-Key: “your_api_key”

3. Server-Side Validation: The API server receives the request and extracts the API key from the specified location (URL parameter, header, etc.). The server checks the validity of the API key by comparing it against a list of authorized keys stored in its database.
4. Authorization Check: Once the API key is validated, the server checks if the associated client or application has the necessary permissions to perform the requested action.
5. Rate Limiting: API keys aid in setting up rate limiting. Rate limiting limits the user’s access to the API based on the rules/policies set by the owner. It also controls the number of requests a client can make within a specific time.
6. Key Rotation and Security Measures: API providers may implement key rotation policies to enhance security. This involves regularly changing API keys to reduce the risk of unauthorized access. It’s crucial to use HTTPS when using API keys to encrypt the communication between the client and the server, preventing interception of the key during transmission.

While API keys are a straightforward authentication method, they have some limitations. One of the main concerns is that API keys can be exposed easily if not handled securely, leading to potential security risks. Therefore, following best practices, such as using HTTPS, avoiding exposure of keys in client-side code, and implementing proper critical management practices, is essential. Other authentication methods, like token-based authentication (JWTs), may be preferred for more sensitive applications.

Token-Based Authentication

Token authentication is more secure than basic authentication since it involves using a unique token generated for each user. JSON Web Tokens (JWT) is a popular token-based authentication method. 

JWTs are self-contained and can store user information, reducing the need for constant database queries. This token is sent with each request to authenticate the user. Token authentication is also a good choice for applications requiring frequent authentication, such as single-page or mobile applications. 

Since the authentication process does not require user passwords in each request, once a user enters the credentials, receive a unique encrypted token valid for a specified session time.it is more efficient and can handle more concurrent requests.

For example:

In this example, the access_token variable is set to a string that contains the token, which is then added to the headers as the Authorization key with the Bearer prefix. The requests. Get() function is then called with the headers to make the request. The response status code is then printed to check whether the request succeeded. 

The client usually obtains the token by requesting a valid username and password to the server. The server will then respond with the token, which the client can use for subsequent requests. The token will have a specific expiration date, after which the client must request a new token from the server. It is recommended to use HTTPS for token authentication, and the token should be encrypted with JWT or OAuth for the production environment.

OAuth 2.0

OAuth 2.0 (Open Authorization 2.0) is a widely adopted and standardized protocol for authentication and authorization in RESTful APIs. It allows users to grant limited access to resources on one site (the resource server) to another site or application (the client) without exposing their credentials. OAuth 2.0 is commonly used for delegated access scenarios, such as when third-party applications need to access user data on behalf of the user.

Here’s an overview of how OAuth 2.0 works:

1. Roles in OAuth 2.0:   

• Resource Owner: The entity that owns the resources being protected (usually the user).
• Client: The application requesting access to the resources of the resource owner.
• Authorization Server: The server is responsible for authenticating the resource owner and providing authorization to the client.
• Resource Server: The server hosts the protected resources that the client wants to access.

2. Authorization Grant Types:

OAuth 2.0 supports multiple grant types, each suitable for different use cases. Standard grant types include:

• Authorization Code Grant: Used by web applications where the client runs on a server.
• Implicit Grant: Suitable for client-side applications, such as single-page apps, where the client can’t keep secrets.
• Client Credentials Grant: Used by confidential clients to authenticate with the authorization server based on client credentials.
• Password Grant: Allows a resource owner’s credentials to be exchanged directly for an access token.

3. Authorization Flow: The authorization process typically involves a series of steps:

• The client initiates the process by redirecting the resource owner to the authorization server’s endpoint.
•  The resource owner authenticates and authorizes the client.
•  The authorization server issues an authorization code or access token to the client.
•  The client uses the authorization code to request an access token from the authorization server.

4. Access Tokens: Access tokens are short-lived credentials that represent the authorization granted to the client. The client includes the access token in the request headers when accessing protected resources on the resource server.

5. Token Refresh: Access tokens have a limited lifespan. To extend the user’s session without re-authorization, the client can use a refresh token to obtain a new access token.

6. Scopes: Scopes define the level of access granted to the client. Clients request specific scopes during the authorization process.

OAuth 2.0 example:

The main disadvantage of this API authentication method is its complexity; it requires multiple steps to grant API access securely and set up API authentication.

REST API Security Best Practices

Here are some best practices that would help you while working with REST APIs:

• Always use TLS
• Use OAuth2 for single sign-on (SSO) with OpenID Connect
• Always use HTTPS to encrypt data in transit.
• Regularly rotate and invalidate tokens to minimize the risk of unauthorized access.
• Implement rate limiting to prevent abuse and brute force attacks.
• Keep authentication logic centralized and avoid hardcoding credentials in the code.
• Use API keys to give existing users programmatic access
• Encourage using good secrets management for API keys

How Do You Select the Most Suitable API Authentication Method?

Securing REST APIs is an ongoing challenge in the fast-growing web development landscape. The authentication method choice depends on your application’s specific requirements, the sensitivity of the transmitted data, and the user experience. By adopting best practices and staying informed about emerging security threats, developers can build robust and resilient systems that protect user data and maintain the integrity of the applications they support. As we navigate the digital age, the importance of secure REST API authentication methods cannot be overstated.

At Knowi

To learn about REST API basics, read our blog post here: REST API Overview. An example of a data analytics tool that supports REST APIs natively is Knowi, a unified analytics platform. You can join your REST API data with data from other applications, SQL or NoSQL databases, flat files, and more. You can then use the dashboard and widget features to build custom visualizations that simplify your data and make them presentable. Still trying to understand? Book a demo today with Knowi and embark on a transformative analytics journey.