Understanding API Authentication Methods

Application programming interfaces (APIs) are essential to the functionality of modern-day applications. However, they often facilitate the exchange of sensitive data, which is why they have become highly targeted by threat actors. Around 60% of organizations have experienced an API-related data breach in the past two years, and of those organizations, 74% have reported having at least three incidents. Mitigating these risks is critical, which has challenged and continues to challenge security teams to prioritize API security now more than ever. Robust API authentication methods play a major role in API security.

API authentication is one of the easiest and most widely implemented ways to safeguard APIs and the data they exchange from threat actors. There are several API authentication methods that developers can choose to implement depending on their individual strengths and weaknesses for certain use cases and applications. In this blog, we will discuss some of the most common API authentication methods.

Basic Authentication

Basic authentication works by sending a username and password encoded in Base64 in the HTTP request headers. While basic authentication is simple to implement and widely supported, it has its drawbacks. Since Base64 is easy to decode, especially for those with the technical expertise to do so, it’s highly susceptible to interception. For that reason, experts recommend that basic authentication should only be used with HTTPS connections.

The HTTPS protocol encrypts any data transmitted between the client and server, which significantly reduces the likelihood of credentials being exposed through interception or man-in-the-middle (MiTM) attacks. Basic authentication, especially when used on its own, is a weak API authentication method in comparison to other methods and should only be implemented independently for very low-security applications.

Multi-Factor Authentication (MFA)

The extra layer of security that MFA adds is a significant step above what basic authentication can offer for APIs. Like its name suggests, it requires multiple forms of authentication to gain access to a system or account. Common MFA methods include:

1. Time-based One-Time Passwords (OTP)
2. SMS or push notifications
3. Hardware security keys
4. Biometrics

MFA is a strong security measure for user authentication; however, its direct application to APIs can be challenging because the majority of MFA methods require user interaction. As you’d imagine, MFA is only a practical API authentication method when users are making the API call. MFA is not a feasible API authentication method for machine-to-machine communications or when an application itself is making API calls.

API Keys

API keys are unique, randomly generated tokens consisting of letters and numbers that are issued to developers or applications to access a particular API. Not only can an API server use the API key to validate the authenticity of the request, but it can also limit the level of access granted, limit its functions to specified parameters, and limit the number of calls a requestor can make. While API keys are relatively easy to implement and manage, they are – in simplest terms – static passwords, making them susceptible to theft, sharing, and misuse. Similar to basic authentication, API keys should not be used alone as the sole API authentication method, especially those that process sensitive data, as this would increase the risk of exposing sensitive data in high-security applications.

Open Authorization (OAuth)

OAuth allows users to grant third-party access to their servers, websites, or applications without sharing login credentials. Rather than exposing usernames and passwords, OAuth uses access tokens to authorize API requests, which is one of the several reasons why it has become the preferred API authentication method. Other important reasons include the following:

1. OAuth tokens prevent sensitive login credentials from being exposed.
2. Users can control the level of access they choose to grant third-party applications.
3. OAuth tokens are temporary and can also be easily revoked.
4. OAuth is a well-established open standard ensuring interoperability between different services and platforms.
5. OAuth authentication processes can easily be analyzed through proper logging and monitoring.

While OAuth is a preferred API authentication method, it’s important to note that incorrectly implemented OAuth flows can pose critical security risks. These risks can be prevented proactively by following OAuth guidelines and regularly conducting security assessments.

OAuth 1.0 vs OAuth 2.0:

OAuth 1.0 was the inaugural version of the standard, initially developed to provide a secure method for applications to access user resources. OAuth 1.0 relies on cryptographic signatures to verify the authenticity and integrity of requests, but OAuth 2.0 is the most common and widely adopted version. It primarily depends on access tokens and does not require cryptographic signing of requests, making it simpler to implement and more flexible than OAuth 1.0. It’s worth noting that OAuth 2.0’s primary focus is authorizing and scoping access to specific resources, not user identity verification.

While OAuth 1.0 offers higher security with its signing process, OAuth 2.0 has largely replaced OAuth 1.0 due to its improved usability, widespread support, and flexibility. Security teams’ choice between OAuth 1.0 and 2.0 depends largely on the compatibility with existing systems or services that are still using OAuth 1.0.

Security Assertion Markup Language (SAML)

SAML is an open standard for exchanging authentication and authorization data between parties, particularly between an identity provider (IdP) and a service provider (SP). SAML makes single sign-on (SSO) possible, enabling users in enterprise environments to access multiple services and applications with a single username and password, essentially eliminating the need for a separate set of credentials or separate log-in process for each service.

While OAuth primarily facilitates authorization and access control, SAML focuses on authentication and identity verification. It is beneficial when identity attributes and assertions are critical for access control decisions. OAuth, however, is ideal for scalable API access control and third-party application integrations. SAML and OAuth can be combined in some cases to address different aspects of authentication and authorization together.

OpenID Connect (OIDC)

OIDC is an authentication protocol built on top of the OAuth 2.0 authentication protocol. ODIC goes beyond OAuth 2.0 by adding an identity layer to the authentication method. This enables developers and security teams to standardize the way applications authenticate users by obtaining their identity information from an authorization server (AS) or an IdP.

OIDC places a strong focus on user consent and control over data sharing. IdPs must request a user’s consent explicitly before granting a client application access to their data. OIDC can be implemented along with OAuth 2.0 to secure APIs’ user-centric applications that need-to-know users’ identities.

Ensuring Robust API Authentication with BreachLock

API authentication methods and security extend beyond initial authentication. To ensure a comprehensive defense, security teams must adopt a holistic approach that includes the discovery, assessment, and continuous monitoring of API use.

Make sure you implement robust API authentication methods the right way. Checkout ultimate API pentesting checklist from BreachLock

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