What Is OpenID Connect (OIDC)? How It Works, Flows, and When to Use It

Every time a nurse taps "Sign in with Google" to access a clinical app, or a warehouse worker logs into a shared terminal at the start of a shift, something has to answer a deceptively simple question: Who is this person, really?

That question trips up a lot of authentication systems. Especially in environments where workers rotate across shared devices, speed matters, and separate credentials for each application create dangerous gaps. According to the Verizon 2024 Data Breach Investigations Report, stolen credentials remain the number one initial action in breaches, appearing in nearly 38% of all analyzed incidents. And yet, most organizations still rely on fragmented login systems that make credential misuse easier, not harder.

That is where OpenID Connect changes the equation.

What is OpenID Connect (OIDC)?

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This blog breaks down how OIDC works, what makes it different from OAuth 2.0 and SAML, which authentication flow fits which application, and what security teams need to know before implementing it.

Why OAuth 2.0 Alone Was Not Enough

To understand OIDC Authentication, you first need to understand what it was built to fix.

OAuth 2.0 handles authorization. It lets an application access specific resources on your behalf, a Google Drive folder, a Salesforce record, without ever seeing your password. It issues access tokens that say "this app is allowed to do X." What it does not do is tell the application who the user behind that token actually is.

That gap created a real-world problem. As platforms like Google, GitHub, and Facebook evolved into identity providers, each of them returned user profile data in a different format. Developers building apps that supported multiple sign-in options had to write custom handling code for each provider. There was no common standard for what a "user identity" looked like in a response.

OIDC was built to close both gaps at once: add authentication to OAuth 2.0, and standardize how user identity data is structured and delivered.

Key Roles in OIDC

Three parties participate in every OIDC transaction:

The OpenID Provider is the core. It handles authentication, manages user consent, and issues the tokens the Relying Party needs to confirm who just logged in.

How OIDC Authentication Works

1. User initiates login: The user clicks "Login" on the Relying Party application.
2. Redirect to the OpenID Provider: The app sends the user to the trusted IdP (Google, Okta, Azure AD, or an enterprise identity system). The user's credentials never touch the application directly.
3. User authenticates: The user enters credentials on the IdP's login page. The IdP may also trigger MFA at this point.
4. Tokens are issued: On successful authentication, the IdP sends back an ID Token, an Access Token, and optionally a Refresh Token.
5. Application verifies and grants access: The Relying Party validates the ID Token, confirms the user's identity, and grants access. It can also call the UserInfo Endpoint to fetch additional profile details.

The entire process completes in seconds. In standard OIDC flows, the application does not directly handle the user’s password.

OIDC Authentication Architecture

An OIDC flow runs across a structured set of components, each with a specific role:

Identity Provider (IdP): Authenticates the user, manages consent, signs tokens, and exposes all endpoints the flow depends on.

Relying Party (RP): The application requesting proof of identity. Redirects the user to the IdP, receives tokens, and validates them before granting access.

Authorization Endpoint: Where the flow begins. The RP sends the user here with the client ID, requested scopes, redirect URI, and a state parameter.

Token Endpoint: Where the RP exchanges an authorization code for tokens. This exchange happens server-to-server, never through the browser.

UserInfo Endpoint: A protected resource the RP calls post-login to retrieve additional profile claims not included in the ID Token.

Browser / User Agent: Carries redirects between the RP and IdP. In a correctly implemented flow, it sees the authorization code but never the tokens themselves.

JWT Validation: The RP fetches the IdP's public keys from the JWKS URI, verifies the token signature, and checks iss, aud, and exp before trusting any identity data.

The trust boundary sits between the Token Endpoint and the RP's backend. Everything passing through the browser before that point should be treated as untrusted until the token signature is verified.

OIDC Tokens: What Each One Does

ID Token: The defining token in OIDC Authentication. A digitally signed JSON Web Token (JWT) that contains verified claims about the user. Core claims include:

The ID Token answers: Who is this user?‍

Access Token: Grants the application permission to access specific resources or APIs. It carries no identity claims on its own. The Access Token answers: what can the app do on the user's behalf?

Refresh Token: A long-lived token that lets the application obtain a new Access Token without asking the user to log in again. It answers: Can we keep this session active securely?

UserInfo Endpoint: After login, the Relying Party can call this protected endpoint using the Access Token to retrieve verified profile data, name, email, locale, and more. This is how OIDC enables personalization without storing credentials.

OIDC Authentication Scopes: What You Can Request

Scopes define what information the Relying Party needs. OIDC standardizes these:

• openid — required; triggers the OIDC flow and ID Token issuance
• profile — name, picture, preferred username
• email — email address and verification status
• address — physical address
• phone — phone number

One of OIDC's biggest improvements over raw OAuth 2.0 is that these scopes are consistent across every compliant provider. No custom format handling per provider.

OIDC Authentication Flows: Which One to Use

The right flow depends on the type of application and where tokens are handled.

Authorization Code Flow + PKCE: The recommended default for most applications today, including SPAs and mobile apps. The user authenticates, the IdP returns a short-lived authorization code, and the app exchanges that code server-side for tokens. PKCE (Proof Key for Code Exchange) adds a cryptographic challenge that prevents authorization code interception attacks. Access and refresh tokens are typically exchanged server-side rather than exposed directly in browser URLs.

Authorization Code Flow (confidential clients): For traditional server-side web applications that can securely store a client secret. Tokens stay server-side, never exposed to the browser.

Implicit Flow: Legacy flow where tokens were returned directly in the browser redirect URL. Now deprecated. The attack surface is too large because tokens are visible in browser history and referrer headers.

Hybrid Flow: Returns the ID Token immediately while using an authorization code for the Access Token. Useful in narrow enterprise scenarios but not recommended for new implementations.

OIDC vs. Other Protocols

OIDC vs. OAuth 2.0: OAuth 2.0 handles authorization only. OIDC adds the identity layer on top. You need both when your application needs to know who the user is, not just that they have permission.

OIDC vs. SAML: SAML uses XML and browser redirects, designed primarily for enterprise web SSO. OIDC uses JSON and REST, works across web, mobile, and APIs. OIDC Authentication is simpler to implement and better suited for modern application architectures. SAML remains common in legacy enterprise environments where migration is costly.

OIDC vs. LDAP: LDAP is a directory protocol for internal network authentication. OIDC works over the internet and supports external identity federation. They can coexist: LDAP handles internal systems, OIDC handles external-facing applications.

Security Considerations Most Implementations Miss

Implementation is not just about making the flow work. It is about closing the gaps that attackers look for.

Token validation: Always verify the ID Token's signature using the IdP's public keys. Check iss, aud, and exp on every token. A token that passes format checks but fails issuer or audience validation is a common attack vector.

Token storage: Store tokens in httpOnly, Secure cookies rather than localStorage. JavaScript-accessible storage is vulnerable to XSS attacks. The token itself becomes the attack surface once the authentication flow is complete.

Nonce validation: Include a unique nonce in each authentication request and verify it in the returned ID Token. This prevents replay attacks where a stolen token is reused.

Logout: OIDC defines both front-channel logout (browser-based session termination) and back-channel logout (server-to-server session revocation). Most implementations only handle local logout, leaving the user's session active at the IdP level. In shared-device environments, this is a significant exposure. A frontline worker who logs out of an app but remains authenticated at the IdP level is still a risk.

Common OIDC Misconfigurations

A correctly designed OIDC flow is secure. A poorly implemented one creates exactly the kind of identity gaps that credential-based attacks exploit.

Accepting unsigned ID Tokens: Always verify the token signature against the IdP's published JWKS keys. An unverified token is an open door.

Not validating the aud claim: Without this check, a token issued for one application can be replayed against another.

Storing tokens in localStorage: Any JavaScript on the page can read it. Use httpOnly, Secure cookies instead.

Incomplete logout: Local sign-out leaves the IdP session active. In shared-device environments, the next user can silently inherit it. Implement both front-channel and back-channel logout.

Over-scoped permissions: Request only the scopes the application actually needs. Every extra scope widens the blast radius if a token is compromised.

Long-lived Refresh Tokens without rotation: A non-rotating refresh token is a standing credential. Rotate on every use.

Improper redirect URI validation: Register exact URIs. Never use wildcards. An open redirect hands attackers the authorization code directly.

OIDC in Operational and Frontline Environments

Standard OIDC implementations assume one user, one device, one session. That assumption breaks down fast in environments like healthcare, manufacturing, and logistics, where multiple workers rotate across the same shared terminals throughout a shift.

In these settings, every session needs to be tied to a verified individual identity, not a shared workstation credential. OIDC's token-based architecture supports this cleanly: each login triggers a fresh authentication against the IdP, issues tokens scoped to that specific user, and can enforce MFA or biometric verification at the IdP level. Properly implemented, OIDC Authentication eliminates the credential-sharing problem that persists on shared devices when older authentication systems are used.

Platforms like OLOID are built around exactly this challenge, applying OIDC-compatible, passwordless authentication to frontline and shared-device environments where traditional login flows create security gaps and friction at every shift change.

How to Implement OIDC: Practical Checklist

Most of these steps are standard across any OIDC deployment. Where they get complicated is in operational environments: shift-based teams, shared terminals, and high-turnover workforces in healthcare, manufacturing, and logistics, where each step below has to account for multiple users on the same device. 

• Choose a certified, compliant IdP (Google, Microsoft, Okta, or an enterprise-grade CIAM platform)
• Register your application with the IdP to receive a client ID and configure redirect URIs
• Request only the scopes your application actually needs
• Implement Authorization Code + PKCE for web and mobile applications
• Validate iss, aud, exp, and signature on every ID Token
• Store tokens in httpOnly cookies, not localStorage
• Implement both local and IdP-level logout
• Use the .well-known/openid-configuration discovery document to dynamically fetch endpoint URLs and public keys
• Rotate client secrets regularly; never expose them in client-side code

In these settings, organizations need additional controls around session attribution, logout enforcement, and per-user authentication. Standard OIDC implementations do not account for this by default. Platforms like OLOID are built to address these operational identity challenges while staying fully compatible with modern OIDC-based authentication architectures.

FAQs

1. What is the difference between OIDC and OAuth 2.0? 

OAuth 2.0 handles authorization: it controls what an application can access. OIDC handles authentication: it verifies who the user is. OIDC is built on top of OAuth 2.0 and adds the ID Token and UserInfo Endpoint that OAuth 2.0 does not provide.

2. Is OIDC the same as SSO? 

OIDC Authentication enables SSO but is not SSO itself. SSO is the outcome: a user logs in once and accesses multiple applications. OIDC is the protocol that makes this possible by letting a single OpenID Provider authenticate the user and share that authentication with multiple Relying Parties.

3. What is an ID Token, and how is it different from an Access Token? 

An ID Token is a JWT that contains verified claims about the authenticated user, such as their identity, when they authenticated, and who issued the token. An Access Token grants access to resources or APIs. The ID Token proves who logged in. The Access Token proves what they can do.

4. When should you use OIDC over SAML? 

Use OIDC Authentication for modern web applications, mobile apps, APIs, and any application requiring JSON-based, REST-compatible identity exchange. Use SAML when integrating with legacy enterprise systems that already rely on XML-based federation and where migration is not practical.

5. Is OIDC secure for shared-device environments? 

Yes, when properly configured. OIDC's token-based model requires fresh authentication for each session. This means each user login against the IdP generates new tokens scoped to that individual. The risk in shared-device environments comes from incomplete logout (leaving an active IdP session after local sign-out) and improper token storage, both of which are addressable at the implementation level.