Complete Guide: SAML vs. OAuth vs. OpenID Connect

You see, I wasted much too much time not understanding these three protocols before it dawned on me. Everybody throws round “SAML” and OAuth and OpenID connect like they are similar, yet they are not. All of them address a different issue, and making the wrong choice can turn your life miserable.

This is what I discovered on building projects with the three.

The Quick Answer (Before We Go Deep)

Imagine it in the following way: SAML is your business badge, which opens the doors to different business offices. OAuth is the key to your car that you hand over to the valet so that he or she can park (but not open the trunk). OpenID Connect is the same as the ID-badge that you show to identify who you are and then that valet-key.

Things are done with different tools.

Side-by-Side Comparison

Feature	SAML 2.0	OAuth 2.0	OpenID Connect
Primary Purpose	Authentication + Authorization	Authorization only	Authentication + Authorization
Best For	Enterprise SSO	API access delegation	Modern web/mobile login
Data Format	XML (verbose)	JSON (lightweight)	JSON (lightweight)
Token Type	SAML assertions	Access tokens	ID tokens + Access tokens
Mobile Support	Poor (browser redirects)	Excellent	Excellent
Implementation Complexity	High	Moderate	Moderate
Certificate Management	Required (X.509)	Optional	Optional
Age	2005 (20 years old)	2010 (15 years)	2014 (11 years)
Enterprise Adoption	~80% of enterprises	Universal for APIs	42% CAGR growth
Federation Support	Native, mature	Limited	Growing (OIDC Federation)

SAML: The Enterprise Workhorse

Big companies use SAML (Security Assertion Markup Language) in cases when they desire one log in it all. You authenticate only once to the corporate Identity Provider, and you are in Salesforce, Workday, your own internal applications, without typing the passwords once again.

Mechanism: The IT department will install an Identity Provider (such as okta or Azure AD). On accessing an app, it redirects you. One authentication is made, an XML assertion is signed and it is trusted by the app. The statement contains who you are and what you are allowed to do.

Why enterprises love it:

• Controlled access of users.
• Deals with old systems that are not auth friendly.
• Inbuilt support of complicated permission arrangements.
• Good compliance audit trails (HIPAA, SOC 2, GDPR)

The painful parts:

• XML is clunky. The size of configuration files is huge and is prone to errors.
• Management of certificates is an ordeal. All the certificates have expiry and once they expire, all falls apart.
• Almost impossible in mobile applications (the browser redirect dance is not very good)
• Spends 300+ hours a year to keep integrations alive.

I have troubleshooted SAML assertion failure at 2 AM. It is worth trusting me that you do not want to be involved in XML signature wrapping attacks or clock synchronization problems unless you are paid to do so.

When to use SAML:

• You have a business that has SAML infrastructure in place.
• You require federalization between institutions (universities, healthcare systems).
• You are connecting to legacy (older .NET applications, ADFS, Shibboleth) systems.
• Adherence needs to be provided with the audit logs and centralized auth.

OAuth 2.0: The Authorization Framework

It is in this point that people get lost: OAuth is not a log-in. It is to provide restricted access to your stuff without providing your password.

Consider the time you had one of these fitness apps connected to your Google Calendar. You are not entering the app with your Google password. You are giving it the permission to read your calendar (and nothing more than your calendar). That’s OAuth.

The functionality: Clicking the option to connect with Google in an app gives you the following question: Hey, should FitnessApp access your calendar? You say yes. Google provides the app with an access token. That token is used to make a call to the Calendar API of Google on your behalf by the app.

Why developers love it:

• API integrations are perfect.
• No passwords flying around (it is a token-based one).
• REST APIs are greatly supported.
• Mobile-friendly

The gotchas:

• OAuth 2.0 had security holes. Implicit grant flow? Deprecated. Open redirector attacks? Common.
• This is resolved by OAuth 2.1 which has made PKCE (Proof Key for Code Exchange) a requirement, eliminated hazardous flows, and mandated a strict match between redirect URI and URI.
• When you implement OAuth yourself, you are likely to get the state parameter wrong and create CSRF vulnerabilities.

When to use OAuth:

• The third-party applications require API access to user data.
• Constructing interconnections across services.
• Mobile applications that make calls to your use the backend APIs.
• Service-to-service call Microservices authorization

OpenID Connect: The Modern Solution

OIDC is OAuth 2.0 over which identity layer has been strapped on. It provides the answer to the question that OAuth had been unable to provide: Who is this person?

Clicks on Sign in with Google on a random site are OIDC. It authenticates you (improves who you are) and the site receives an access token (so that it can make use of the Google API to retrieve your profile picture).

Mechanism: It is an OAuth flow, but you receive an ID token as well; a JSON Web Token (JWT) which states: This is John Doe, email john@example.com, verified by Google. The app verifies the signature of the token, and it is aware of the fact that it can trust the identity.

Why it’s taking over:

• Less complicated than SAML (JSON rather than XML)
• Deals with authentication and authorization.
• Performs well with mobile, web and single page applications.
• Support of social logins (Google, GitHub, Facebook)
• The automatic provider configuration discovery.

The learning curve:

• You must ensure the proper validation of ID tokens (signature, issuer, audience, expiration).
• OAuth 2.1 token rotation (Refresh token) needs to be implemented with caution.
• Linking accounts may cause account vulnerability, which comes with mixing several identity providers.

When to use OIDC:

• Creation of web or mobile applications of the current era.
• You desire Sign in with Google/GitHub/Microsoft.
• Business and consumer SaaS.
• Cloud-native applications and services.
• Anywhere that you are using SAML and not limited by legacy.

Complexity of implementation Real Talk.

SAML: Expect 2-4 weeks when doing it from scratch. You will struggle with metadata files, generation of certificates and XML namespaces. Minimum use a library (passport-saml with Node.js, Spring Security with Java) and you will despise yourself.

OAuth 2.1: Maybe a week with current libraries. The protocol is not that difficult but getting it stored. Don’t skip PKCE. Don’t put tokens in URLs. Check yes To use refresh token rotation.

OIDC: Least amount of time to implement, possibly 3-5 days. A majority of complexity is handled by the libraries. The problem is the ID token validation, fail to check one of them (such as checking whether the nonce is correct) and you are at risk.

Security: What Actually Matters

All the three are secure when applied properly. That’s a massive “if.”

SAML vulnerabilities:

• XML Signature Wrapping (attackers edit the assertions post-signing)
• Replay attacks (recidivism)
• Mishandling of the certificates (expired certs destroy it all)

OAuth 2.0/2.1 vulnerabilities:

• Open redirector attacks (lax redirect URI validation)
• CSRF through absence of state parameter.
• Token leakage (Browser history bearer tokens)

OIDC vulnerabilities:

• ID token validation errors (acceptance of tokens of incorrect issuers)
• Issues of nonce and session fixation.
• Several identity providers Account linking during the support of multiple identity providers.

The pattern? Major breaches are based on implementation errors rather than the protocols.

The Hybrid Reality

Majority of the organizations do not choose only one. A typical 2025 setup:

• SAML to allow internal and legacy applications to be accessed by employees.
• OIDC to contemporary cloud applications, customer products.
• OAuth 2.1 based on API authorization and third party integrations.

Achieving 85% credit breach reduction and 40% reduction in support costs, according to the recent enterprise studies with this combo.

My Recommendation

Starting fresh? Use OIDC. It is contemporary, actively developed and covers 90 percent of the usage.
Already have SAML? Retain it as enterprise SSO, however, new apps should be added to OIDC.
Building APIs? No exceptions, OAuth 2.1 with PKCE.

Need to support everything? Only use an identity broker (Auth0, Okta, BoxyHQ) to interoperate between protocols. The implementation of OIDC is done once with a SAML customer being dealt with by the broker.

The protocols are not going anywhere. SAML is 20 years old and is still prevailing in enterprises. OAuth and OIDC are those that are developing rapidly. Know what each of them is really good at, and you will save yourself a few more weeks of misery.

Read:

Authentication Methods and Protocols: A Guide for Confused Developers