OAuth2 & OpenID Connect Deep Dive · Lesson

Multi-Factor Authentication (MFA)

Explore how MFA integrates with OIDC flows to add an extra layer of security to user authentication.

Multi-Factor Authentication (MFA) is a free OAuth2 & OpenID Connect Deep Dive lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the OAuth2 & OpenID Connect Deep Dive learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

What is Multi-Factor Authentication?

Multi-Factor Authentication (MFA) adds an extra layer of security to user accounts beyond just a password.

Instead of relying on a single piece of evidence (like "something you know"), MFA requires two or more verification methods from different categories.

The "Factors" of MFA

MFA typically combines factors from these categories:

Something you know: A password or PIN.
Something you have: A phone, hardware token, or authenticator app.
Something you are: A fingerprint, face scan, or voice recognition.

Using multiple factors makes it much harder for unauthorized users to gain access.

Why MFA in OIDC?

OpenID Connect (OIDC) itself doesn't perform MFA. Instead, it acts as a secure way for an Identity Provider (IdP) to tell your application whether a user authenticated with MFA.

Your application can then use this information to make informed authorization decisions.

Introducing ACR Values

In OIDC, "Authentication Context Class References" (ACR values) are used to specify how a user was authenticated.

These are unique identifiers that represent different levels or methods of authentication, including whether MFA was used.

Requesting a Specific ACR Level

When your application initiates an OIDC authorization request, it can include the acr_values parameter.

This parameter tells the Identity Provider that your application prefers or requires a specific authentication context, such as MFA.

Example: Requesting MFA

Here's a simplified example of an OIDC authorization URL requesting an MFA context. The specific acr_values like "mfa" or "https://acr.example.com/mfa" depend on the Identity Provider's configuration.

public class Main {
  public static void main(String[] args) {
    String authUrl = "https://idp.example.com/authorize?"
      + "response_type=code"
      + "&client_id=my_client_app"
      + "&redirect_uri=https://app.example.com/callback"
      + "&scope=openid%20profile"
      + "&acr_values=mfa";
    System.out.println("Authorization URL:\n" + authUrl);
  }
}

Receiving MFA Status in the ID Token

After successful authentication, the Identity Provider returns an ID Token to your application. This token contains various claims about the user and their authentication session.

The acr claim within the ID Token indicates the actual authentication context class reference that was satisfied.

Example: Decoding an ID Token with 'acr'

Let's imagine an ID Token payload after a user authenticated with MFA. The acr claim would be present, confirming the authentication method used.

In a real application, you would decode and validate the JWT to read this claim.

public class Main {
  public static void main(String[] args) {
    // Example of a decoded ID Token payload
    // In a real app, you'd parse a JWT.
    String idTokenPayload = "{\n  \"iss\": \"https://idp.example.com\",\n  \"sub\": \"user123\",\n  \"aud\": \"my_client_app\",\n  \"exp\": 1678886400,\n  \"iat\": 1678882800,\n  \"auth_time\": 1678882700,\n  \"acr\": \"mfa\",\n  \"amr\": [\"pwd\", \"otp\"]\n}";
    System.out.println("Simulated ID Token Payload:\n" + idTokenPayload);
  }
}

Enforcing MFA-Based Policies

Once your application receives and validates the ID Token, it can check the acr claim.

Based on this, you can implement conditional access policies. For example, if a user tries to access sensitive data, and the acr claim doesn't indicate MFA, you might deny access or prompt for re-authentication.

Quick Check

Which OIDC parameter is used by a client application to request that a user authenticates with Multi-Factor Authentication?

Recap: MFA & OIDC

We've learned that MFA adds critical security layers by requiring multiple authentication factors.

OIDC doesn't perform MFA itself, but it provides a standardized way (via acr_values in requests and the acr claim in ID Tokens) for applications to request and receive information about the authentication context, enabling robust, MFA-aware security policies.

Frequently asked questions

Is the “Multi-Factor Authentication (MFA)” lesson free?

Yes — the full text of “Multi-Factor Authentication (MFA)” is free to read here on the web, and the OAuth2 & OpenID Connect Deep Dive course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the OAuth2 & OpenID Connect Deep Dive course, upgrade to CoddyKit PRO.

What will I learn in “Multi-Factor Authentication (MFA)”?

Explore how MFA integrates with OIDC flows to add an extra layer of security to user authentication. You practise OAuth2 & OpenID Connect Deep Dive with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start OAuth2 & OpenID Connect Deep Dive?

No prior experience is required. OAuth2 & OpenID Connect Deep Dive on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Multi-Factor Authentication (MFA)” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this OAuth2 & OpenID Connect Deep Dive lesson?

Yes. Every OAuth2 & OpenID Connect Deep Dive lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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