Organizations want to streamline the user experience, allowing users to access multiple applications and websites by logging in only once. They may also want to reduce the number of disparate authentication and authorization silos for ease of management and to enforce standard policies.

Authentication and authorization frameworks such as OAuth and SAML can help organizations build secure and standard authentication and authorization flows.

What is Authentication

Authentication is the process of confirming a user’s identity or asking, "Are you who you claim to be?". An example of authentication is when you visit and go to log in. The site asks you for your email and password then it'll confirm your credentials by matching them in the database (usually). If this fails, the site will return an error.

Authentication vs. Authorization

While Authentication verifies the user's identity, Authorization validates that they have access to the resources they are accessing, or asking, "Are you allowed to do/access this?". Unlike authentication, which we can interact with through login forms, authorization is usually handled on the backend, so attacking it requires a different perspective and techniques that assess how access control is handled in the web application. The graphic below shows some key differences between authentication and authorization.



Broken Authentication

It's not uncommon to find incorrectly implemented authentication mechanisms. The impact of this ranges from the disclosure of sensitive information to the compromise of the underlying OS. If we compromise an application's ability to identify the requesting user via its API, this compromises the overall web application security.

Authentication can be compromised in many ways, including:

  • Brute-forcing the login page (credential stuffing) with a list of usernames and passwords.
  • Manipulating unsigned or weakly signed session tokens such as JWT.
  • Exploiting weak passwords and encryption keys.
  • Obtaining authentication tokens and passwords from a URL.

The Broken Authentication module covered basic techniques to attack authentication mechanisms, and this module will focus on some of the more advanced authentication attacks.


A JSON Web Token (JWT) is an open standard used to create access tokens for an application. The JWT is created with a secret key that is private to the application. When an application receives a JWT from the user, it verifies that it was created with this secret key.

Any modification to the JWT without this key will result in verification failure. JWTs can be decoded as its encoded in base64 format. The website can be used to decode a JWT.

In the upcoming sections, we will cover how the JWT authentication flow works and the multiple attacks that can be used to exploit it.


Open Authorization (OAuth) is an open standard authorization framework. OAuth is used by platform applications and services, such as Google, Microsoft, GitHub, and Facebook, to provide delegated access to client applications using access tokens. In this way, an end user can access the client application without sharing their login credentials with the client.

OAuth can provide a large attack surface due to implementation flaws. Attacks on client applications can result in gaining access to confidential resources such as email (including email archives), communication and collaboration systems, and more. We will discuss OAuth flow in the upcoming sections and will cover multiple attacks to exploit it.


OAuth is not an authentication protocol. It effectively decouples a user's credentials from their requests to consumable resources. Instead, organizations may use LDAP (commonly Active Directory), Security Assertion Markup Language (SAML), or Central Authentication Service (CAS) to implement standard authentication schemes such as Single Sign On (SSO) for web applications. CAS is an open-source authentication protocol for implementing a standards-based single sign-on (SSO) for Web applications. It is one of many authentication protocols that can be integrated with authorization capabilities.

With SSO, a user logs into one application and can sign into other applications automatically, regardless of the domain the user is in or the technology in use. SAML implementations are often overlooked in most SSO applications due to the protocol's security. But there are some issues that may arise during the implementation of the SAML protocol.

Successful exploitation of SAML attacks results in authentication bypass, remote code execution, and unauthorized access to server resources, which we will cover in upcoming sections.