October 12, 2023
12 min read

Common API Authentication Methods: Use Cases and Benefits


As businesses expand and gain visibility, it’s natural that their API attack surfaces become more exposed — increasing the risk of dangerous data breaches. Protecting cloud communications and securing data in transit should be your organization’s top priority.

API authentication mechanisms help ensure that only valid users can access your application's features and services, and these mechanisms should be tailored to fit your specific needs. With some examination of your internal framework, you can access a much greater level of security, both for your application’s infrastructure and for your users.

What is API authentication?

APIs provide connectivity between applications, allowing them to exchange data and services quickly. However, because APIs have become a target for hackers as organizations scale their applications, development teams must find a way to authenticate users before they can access the application’s services. Authentication practices confirm that the user is who they claim to be, instead of allowing attackers to pose as valid users with their stolen credentials.

API authentication is a process that uses software protocols to validate the identity of users attempting to make a connection to the application. When a user makes an API call, the protocol sends the login credentials to a remote server in encrypted form to verify that users are who they claim to be and determine whether or not to grant them access. If a set of credentials is determined to be faulty, the protocol will block access to the API to defend it from potential malicious intent.

Authentication is the process of validating identities in the eyes of an organization, which provides a vital layer of security to APIs.

Basic Authentication

HTTP Basic Authentication is by far the simplest approach to authentication. This method sends a username and password alongside every API call with an HTTP header for transmission. No session IDs, login pages, or cookies are required, making it a very straightforward and accessible solution for anyone.

Pros and cons of Basic Authentication


  • Ease of implementation — The biggest (and as some would say, only) argument in favor of HTTP Basic Authentication is its simple implementation and overall compatibility with systems. 


  • Fragility — Basic Authentication is rarely recommended as a standalone authentication solution anymore because credentials are not encrypted. Anytime a username and password pair is shared, it introduces risk for attackers to intercept them and perform malicious actions like man-in-the-middle attacks. 
  • Logout functionality — Logout function is not supported, and although there are ways to avoid this hiccup, methods vary from browser to browser and may not be supported at all. 
  • Password reset — It’s difficult to reset passwords under Basic Authentication implementations, which poses security trouble should a user lose their credentials. 

Protect Mission-Critical APIs & Services: Efficient protection strategies revealed

API keys

An API key is a unique identification code that is used to authenticate an API user. API keys are one of the most fundamental elements of API authentication because they are assigned to each API user to ensure specific access mechanisms.

When a user wants to request access to an API, they submit a unique API key to the security solution. (Keep in mind that first-time users need to receive an API key after their identity has been validated by other processes.) If the API key is valid, the solution grants access — if not, it denies access. This process occurs within a matter of seconds, making it a useful tool for development teams wanting to streamline their security protocols. 

Use cases for API keys

On top of being one of the most straightforward and effective authentication protocols, API keys are used to control and manage access to the API’s interface. Development teams can gain insight into how and why their applications are being accessed so they can get ahead of any malicious activity or misuse of power. 

API keys don't just identify and authorize users, but projects as well. They can determine if an application making a call has been authorized by checking if the API is enabled in the project. This process gives development teams flexibility to limit API use to a specific environment and consolidate usage information. Most importantly, API keys can reject any calls made from projects that don’t have proper access.

Pros and cons of API keys


  • Stronger than HTTP — API keys are a step above HTTP Basic Authentication since they are typically very difficult to guess — especially if they’re longer. 
  • Traffic control — API trends let clients control the number of calls made to their APIs, block anonymous traffic to troubleshoot or debug issues, and analyze trends in API traffic.
  • Filtering — Using API keys, clients can filter logs with ease. 


  • Lacks authorization — The major downside of API keys is that they’re not foolproof for authorization purposes, meaning that an attacker who gains hold of an API key can access all of an application’s data and services. 
  • User identification — API keys can only identify projects, not individual users.
  • Project creation — API keys cannot determine the creators of a project.

Digest Authentication

Digest Access Authentication allows service providers to verify an individual's credentials using a web browser. Think of it as a slightly stronger version of Basic Authentication that doesn’t require a password to be transmitted. Used by both HTTP and SIP, Digest Authentication saves an encrypted version of a username and password to a server so that clients cannot send their passwords in a format decipherable by attackers. More specifically, it attaches hash values to a set of credentials so the server can authenticate without a user having to send a password in plaintext.

Pros and cons of Digest Authentication


  • Encryption — You can send a hash-encrypted version of a password to the server instead of plaintext
  • RFC 2617 nonce — Get ahead of malicious threats using RFC 2617 nonce.
  • Check client attributes — Use a server to check a client’s nonce attributes with timestamps. 
  • Prevent repetition — You can maintain a list of nonce values and apply hash values to prevent repeats. 


  • Attack surface — Digest Authentication is still vulnerable to man-in-the-middle (MitM) attacks because attackers can instruct clients to use Basic Authentication.
  • Server identification — Clients cannot verify the server’s identity.
  • Mixed modes — Some security protections are discretional, meaning clients can operate in less secure modes.
  • Reversible encryption — Passwords can be stored using reversible encryption, which may inadvertently give attackers access to plaintext passwords.

OAuth 2.0

OAuth 2.0, or Open Authorization, is the industry standard for online authorization. The protocol is designed to let applications securely access resources hosted by other web apps and control access to their resources — all without revealing credentials. OAuth 2.0 restricts the actions an app can perform on behalf of a user through its use of consented access.

How does OAuth 2.0 work?

It’s important to remember that OAuth 2.0 is an authorization protocol and not an authentication protocol — meaning that its main function is to grant access to resources like user data or applications. To do this, it uses access tokens, or bits of data that signal a user’s authorization, that can be inserted with data to be even more secure. 

In the OAuth flow, the client initiates an authorization request from the server by providing a client ID for identification. The authorization server then authenticates the client and confirms they can access the set of resources they are requesting. The server contacts the owner of the resources to confirm authorization and returns to the client with an access token or authorization code. Finally, the client can request access to the resources in the resource server using their new access token.

Pros and cons of OAuth 2.0


  • Versatile — OAuth 2.0 is adaptable to any solution because it includes tokens in HTTP / HTTPS headers, including websites, plug-ins, and mobile and desktop applications. 
  • SSL — The protocol relies on Secure Sockets Layer (SSL) to ensure encryption and save user access tokens.
  • Secure access — OAuth 2.0 limits access to user data and shares it without releasing credentials or personal information.


  • Mixed services — Each service requires its own implementation, meaning you may need to write separate pieces of code for every extension.
  • Verification requests — To verify users, you may have to make multiple requests to get the information you need.
  • Horizontal structure — The central hub and account are connected, which means that if either one is hacked, more than one site will be affected.
  • Token data — If an attacker steals a token, they will briefly gain access to the secure data in the token.

JWT (JSON Web Tokens)

JSON Web Token (JWT) is an open standard that offers a safe and secure way for transmitting information between parties as JSON objects. JWTs store encrypted user data and transmit it between applications as needed. They are small in size, so they can be sent inside HTTP headers or through URLs quickly. These tokens can be signed so that clients can inject them with additional data once a user has been authenticated, and they contain all required information about a user or entity so that querying the database multiple times isn’t necessary.

Pros and cons of JWT


  • Simple implementation — JWT signing algorithms are much more straightforward than those of XML and do not present as many security vulnerabilities. 
  • Token size — JWTs are smaller than SAML tokens when encoded, making them ideal for HTTP and HTML environments. 
  • Ease of use — Recipients of JWTs do not need to call a server to validate the tokens. JWTs can also be invalidated easily.
  • Widespread use — JSON parsers are easy to work with because they have an obvious document-to-object mapping in most programming languages.


  • API call size — Every API request must carry the JWT in its headers, which increases the size of the network request payload. This means that most API calls will be larger using JWTs.
  • Key security — If the access key for a token is compromised, then an attacker can access the entire system. This puts extra pressure on the security management of keys and those who can access them.
  • Active user count — Servers cannot monitor user status when a token is issued. Instead, users must update their tokens before servers can obtain this information, meaning that a server cannot pinpoint how many active users they have in the application.
  • Backend management — Client management from the backend may be more difficult because a user must be assigned a new JWT from the server before it can edit or update their access privileges.

OpenID Connect

OpenID Connect (OIDC) is an open standard authentication protocol that is built and layered on top of the OAuth 2.0 framework. It provides a streamlined way for third-party applications to validate a user’s identity and collect basic user profile information without the need for specific credential management. OIDC uses JSON web tokens (JWTs) to access protected resources and inform the API server that user authorization has been granted.

OpenID Connect vs. OAuth 2.0

While OAuth 2.0 and OIDC work in tandem, the former is focused on resource access while the latter targets user authentication. OIDC streamlines the login process for users so that any time they need to enter a website, they are redirected to the OpenID site to log in. The user is then sent back to the website after OAuth 2.0 is authorized to review their information. Once authentication occurs, the user receives an access token. 

Pros and cons of OpenID Connect


  • Easy storage — Users do not need to store credentials in their systems because they can rely on OpenID to store information for them when connecting to multiple sites.
  • Offload authentication — Clients can leave user authentication to OpenID providers with robust security systems when logging users into their sites. 
  • Simple implementation — OpenID can be a more straightforward process than hybrid implementations of OAuth. 


  • User data management — Because OpenID is an authentication service and not an authorization system like OAuth, it cannot make signed requests to receive, delete, or edit user information. 
  • Lateral attacks — While OpenID is very secure, if an attacker gains access to a user’s OpenID credentials, they can move across networks, making them difficult to locate or block.
  • Extensions — Support for OpenID extensions — and information you can access through these extensions — will vary from provider to provider.

HMAC (Hash-Based Message Authentication Code)

Hash-Based Message Authentication Code (HMAC) is a message encryption method that uses a cryptographic key and a hash function. This authentication solution gives servers and clients a private key that only they know, called a shared secret — a more secure encryption technique than the original Message Authentication Code (MAC). In an HMAC transaction, the client and server can decode transaction messages using their secret keys and hash functions.

Pros and cons of HMAC


  • Smaller attack surface — HMAC permanently hashes a message so it can only be accessed with the secret key. This security technique is effective in lowering the risk of malicious attacks or security breaches like man-in-the-middle attacks or replay attacks.
  • Compliance — HMAC’s cryptographic algorithm helps organizations comply with standards like GDPR by only allowing your application to interact with trusted services.
  • Straightforward integration — HMAC is widely used and supported by many programming languages, making for easy integration with your existing workflows.


  • Key management — Because HMAC relies on a secret key, attackers can compromise entire systems if they get their hands on it. As such, your organization needs to have an airtight key management process.
  • Early detection — HMAC is slightly limited in its ability to detect message tampering, so it should be deployed alongside other security protocols to establish well-rounded application security. 
  • Attack prevention — HMAC may be able to identify certain attacks in advance, such as reply attacks, but it may not be able to prevent them.

Mutual SSL/TLS Authentication

If you’ve done any research on secure online transactions, chances are you’ve heard of Secure Socket Layer (SSL) protocol. With SSL, a browser attempting to connect to a secure server can verify the server’s certificate using public key and private key encryption. Clients can also use Mutual Authentication to make sure both they and the server use signed certificates to cross–authenticate and verify the other party’s identity. 

While Mutual Transport Layer Security (mTLS) is also a cryptographic protocol that authenticates data transfer between servers, applications, and users, it’s an upgraded version of SSL. This protocol establishes an encrypted TLS connection that gives both parties respective digital certificates they use to authenticate each other. mTLS is frequently used in a Zero Trust security framework for devices and users within an organization while keeping APIs secure by strengthening an application’s cloud environment.

Pros and cons of Mutual SSL/TLS Authentication

Pros of Mutual SSL/TLS

  • Secure data transfer — Without mutual authentication, it’s possible for attackers to intercept and change data going to and from the web server. SSL / TLS prevents malicious attacks with cryptographic protocols. 
  • User verification — SSL / TLS verifies that your website users are who they say they are before making online transactions, ensuring you can do business safely.
  • Reliability — Mutual SSL and TLS are widely trusted protocols, meaning you’ll earn the trust of your customers and business partners.

Cons of Mutual SSL/TLS

  • Initial cost — Getting certified for mutual SSL / TLS is no small task. As such, the initial price of the certificate may seem high, but the security features pay for themselves in no time.
  • Mobile implementation — SSL / TLS were originally intended for web applications, and some mobile configuration abilities still lag. Despite potentially pesky setup and module requirements for mobile, SSL / TLS authentication is still the way to go.
  • Mode transition — While moving over to SSL / TLS, some of your files may continue to be served via HTTP. Your users may get a warning message about their data security, which can confuse them. 


When choosing the right API authentication mechanism for your company, you must remember that API authentication is not the same as API authorization. Authentication validates your user’s identity, and authorization confirms that the user can access your application.

Authentication is a crucial aspect of API security because it protects your application services and ensures that only approved users, servers, and applications can make API calls to your servers. To choose the right mechanism for you, you should determine which methods fit into your API framework and infrastructure. Then, choose the solution that gives you well-rounded security without overwhelming your development teams. 

Kong’s cloud native API platform seeks to make these processes easier for you. With services like authentication mechanisms and secure data transmission, we make your API security strategy bulletproof — and give your time back so you can focus on your product and business solutions.

To learn more about how to boost your application development, request a demo from Kong today.