Analysis of Common Federated Identity Protocols: OpenID Connect vs OAuth 2.0 vs SAML 2.0


Federated Identity

Single Sign-On (SSO)

Authentication vs. Authorization

OAuth 2

  • Resource owner: the user that can grant access to the protected resource
  • Client: the application that requests access to a protected resource
  • Resource Server: the server that hosts a protected resource
  • Authorization Server: the server that authorizes the client to access a protected resource
  • Authorization Code Grant Type
  • Implicit Grant Type
  • Resource Owner Password Credentials Grant Type
  • Client Credentials Grant Type
  • First, the Client (application) spawns a browser window similar to the one from Figure 1 asking for Resource Owner’s authorization to proceed further.
  • Once the Resource Owner approves the access the Client receives a verification code -a simple randomly generated string.
  • The Client requests an Access Token from Authorization Server by providing the verification code acquired in the previous step.
  • If the verification code is correct the Authorization Server generates an Access Token and sends it to the Client.
  • The Client makes an HTTP request to access the protected resource located on the Resource Server including the Access Token in the request.
  • If the Access Token is valid the Client is allowed to access the protected resource.

OAuth 2.0 vulnerabilities

Account Takeover via Open Redirect's verification code


Account takeover via CSRF<attacker’s authorization code>



OpenID Connect

OpenID Connect vs. OAuth 2.0

SAML 2.0

SAML Vulnerabilities

XML Signature Wrapping

SAML Authentication Bypass

  1. The attacker logs into his account ( and tries to access a resource.
  2. The Identity Provider generates a SAML assertion containing the user identifier (email address) and sends it back to the Service Provider.
  3. Now the attacker updates his email address in the SAML assertion, and adds an XML comment right before
  4. Due to an XML parsing issue the SAML Processing Library ignores the comment and everything after it. Thus, the Service Provider processes as the real email address of the attacker instead of
  5. As a result, the attacker is allowed to access the protected resource on behalf of


SAML vs. OpenID Connect vs. OAuth 2




Co-founder and CEO of HackEDU. Previously a CISO. 15 years in cybersecurity.

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Jared Ablon

Jared Ablon

Co-founder and CEO of HackEDU. Previously a CISO. 15 years in cybersecurity.

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