Category: FIDO & Passkeys

Authentication Ceremony

Also known as: WebAuthn Authentication Ceremony

Simply put

An authentication ceremony is the coordinated sequence of steps in which a user and their device work together to prove the user's identity to a website or application using a previously registered credential. It is one of the two ceremonies defined in the WebAuthn specification, the other being registration. During this process, the device uses the credential to respond to a challenge from the service, confirming the user without necessarily sending a shared secret like a password.

Formal definition

In the WebAuthn specification, an authentication ceremony is the defined interaction in which a user, the user's client platform, and at least one authenticator act in concert to authenticate the user against a previously registered public key credential. Per the WebAuthn flow, the relying party issues a challenge; the authenticator produces an assertion by signing over the challenge and related data with the private key corresponding to the registered credential, and the relying party validates the returned signature. The ceremony encompasses challenge setup, signature validation, and signature counter handling as described in the specification. It should be distinguished from the registration ceremony, which enrolls a new credential rather than exercising an existing one. Note that this term is specific to WebAuthn and denotes the runtime authentication step; it does not by itself address authorization or identity governance concerns, which are out of scope here.

Why it matters

The authentication ceremony is the runtime moment where WebAuthn delivers its core security benefit: proving a user's identity through a challenge-response signed by a private key that never leaves the authenticator, rather than transmitting a shared secret like a password. In most deployments this design means the relying party never receives a reusable secret it could leak, and there is no password on the wire for an attacker to intercept or replay. For architects evaluating phishing-resistant authentication, understanding the ceremony matters because its security depends on correct implementation of the specification's steps rather than on the mere presence of a credential.

Because the ceremony encompasses challenge setup, signature validation, and signature counter handling, mistakes at any of these points can undermine the assurance the mechanism is intended to provide. A relying party that fails to validate the returned signature correctly, or that mishandles the challenge, effectively negates the guarantees WebAuthn is designed to offer. Signature counter handling, where supported by the authenticator, can help a relying party detect certain anomalies, though its behavior varies by authenticator and deployment.

It is also important to scope the term accurately. The authentication ceremony addresses only the runtime step of proving who the user is against a previously registered public key credential. It does not by itself determine what that user is permitted to do, nor does it cover identity governance concerns such as provisioning or access reviews. Treating a successful ceremony as if it resolved authorization would conflate two distinct steps and is out of scope for this term.

Who it's relevant to

IAM Engineers and Identity Architects

Engineers implementing WebAuthn-based authentication need to understand the ceremony's discrete steps, challenge setup, signature validation, and counter handling, because assurance depends on correct relying-party implementation rather than on the presence of a credential alone. Correctly distinguishing the authentication ceremony from the registration ceremony is essential to designing flows that exercise existing credentials versus enrolling new ones.

Security Architects

Architects evaluating phishing-resistant authentication should understand that the ceremony's challenge-response model avoids transmitting a shared secret, which in most deployments removes the password from the wire. This informs decisions about where WebAuthn fits within a broader authentication strategy, while recognizing that the ceremony addresses authentication only and does not resolve authorization.

System Administrators

Administrators operating services that rely on WebAuthn benefit from understanding what a successful authentication ceremony does and does not establish. It confirms the user against a previously registered credential at runtime but leaves access decisions and lifecycle management to other components and processes.

Inside Authentication Ceremony

Ceremony participants

The parties involved in the authentication ceremony, typically the human user (claimant), a client or user agent (such as a browser or authenticator), and the verifying party (relying party or identity provider). The concept extends the notion of a protocol beyond machine-to-machine messages to include the human and their actions.

Human actions and interactions

The out-of-band, human-performed steps that a purely technical protocol description omits, such as reading a screen, entering a credential, tapping a security key, presenting a biometric, or verifying a prompt. These actions are treated as in-scope steps of the ceremony rather than assumed to be reliable inputs.

Trust and verification boundaries

The points where the human must make a trust decision, for example confirming a domain, verifying a device, or approving a push notification. These boundaries are where usability and security assumptions can break down, so the ceremony makes them explicit.

Credential presentation and factors

The mechanism by which the claimant proves an authentication factor during the ceremony, spanning knowledge, possession, and inherence factors. In FIDO2/WebAuthn ceremonies, for example, this includes user gestures such as a touch or biometric that authorize the use of a possession-based authenticator.

Ceremony outcome

The result the ceremony produces, typically a verified authentication event that the relying party can rely upon. This is distinct from authorization; establishing who the principal is does not by itself determine what that principal may do.

Common questions

Answers to the questions practitioners most commonly ask about Authentication Ceremony.

Is an authentication ceremony the same thing as the authentication protocol itself?

No. The authentication ceremony refers to the human-facing interaction and the sequence of steps a user actually performs and perceives, whereas the underlying protocol (for example WebAuthn or a SAML 2.0 flow) is the machine-to-machine exchange that carries out the verification. The ceremony includes the user-visible actions and prompts around the protocol, not just the protocol messages. Conflating the two obscures usability and security issues that arise specifically at the human-interaction layer.

Does completing an authentication ceremony mean the user is also authorized to access the resource?

No. An authentication ceremony establishes who the principal is; it does not determine what that principal may do. Authorization is a separate step that typically occurs after authentication succeeds, and it is governed by whatever access control model the deployment uses (such as RBAC, ABAC, or ReBAC). A successful ceremony can produce an authenticated session or token, but access decisions still require a separate authorization evaluation.

What design factors typically influence how an authentication ceremony is structured?

In most deployments, the ceremony's design depends on the factors being verified (knowledge, possession, or inherence), the protocol in use, and the target platform's user-interface constraints. Considerations often include how prompts are presented, how the user selects or confirms a credential, how errors and fallbacks are handled, and whether step-up authentication may be triggered mid-flow. The exact structure varies by vendor and by the standard profile implemented.

How does the authentication ceremony relate to FIDO2 and WebAuthn implementations?

In WebAuthn-based flows, the ceremony typically encompasses the user-visible steps such as invoking the authenticator, performing a user gesture or biometric check, and confirming the credential to be used. WebAuthn specifications commonly distinguish registration and authentication ceremonies as defined interaction sequences. The precise user experience depends on the platform, the authenticator type, and the relying party's configuration.

What are common points of failure in an authentication ceremony?

Failure points frequently occur at the human-interaction layer rather than in the cryptographic protocol itself. Examples can include user confusion during credential selection, mishandled fallback paths, unclear error messaging, and susceptibility to social engineering or interface manipulation. Because these depend on how the ceremony is presented and implemented, addressing them is largely a matter of user-experience and deployment design rather than protocol changes alone.

How should step-up authentication be incorporated into an existing ceremony?

Step-up authentication is typically introduced as an additional ceremony triggered when a higher assurance level is required for a specific action, rather than replacing the initial authentication. In most deployments this means the user completes a further verification step (often an additional factor) mid-session. The exact triggering logic, the factors requested, and how the elevated state is represented in the resulting session or token depend on the vendor, profile, and policy configuration.

Common misconceptions

An authentication ceremony is just another name for an authentication protocol.

A ceremony deliberately extends the protocol concept to include the human participant and their out-of-band actions. A protocol specification typically models only the messages exchanged between technical endpoints, whereas a ceremony also accounts for human steps, interfaces, and trust decisions that fall outside the protocol's formal scope.

The human steps in a ceremony are reliable and can be treated as trusted inputs.

The ceremony framing exists precisely because human actions are error-prone and subject to manipulation, for example phishing or prompt fatigue. Modeling these steps explicitly is intended to surface where usability and security assumptions may fail, rather than to assume they hold.

A successful authentication ceremony means the user is authorized for what they are trying to do.

An authentication ceremony concerns verifying who the principal is, not determining what they may access. Authorization is a separate step that follows successful authentication, and it is out of scope for the ceremony itself.

Best practices

Model the human participant and their actions explicitly as part of the ceremony, rather than limiting analysis to the technical protocol messages exchanged between endpoints.

Identify each point where the human must make a trust decision, and design the interface so that the correct decision is the easy and obvious one.

Prefer phishing-resistant ceremonies, such as FIDO2/WebAuthn flows that bind the credential to the origin, to reduce reliance on the human to verify domains or detect deception.

Account for human failure modes such as prompt fatigue and misdirected credential entry when evaluating the security of a ceremony, and treat these as in-scope risks.

Keep the authentication ceremony's scope focused on establishing identity, and handle authorization decisions as a distinct subsequent step.

Validate that each factor presented during the ceremony maps to its intended category (knowledge, possession, or inherence) so that the ceremony delivers the assurance level the deployment requires.