What are allowCredentials in WebAuthn?

In WebAuthn, allowCredentials is a crucial field in the PublicKeyCredentialRequestOptions object (in developer forums, it's also often called allowList or WebAuthn allowList). It's used during the authentication (login) process to specify which registered credentials can be used to authenticate a user. This field contains a list of PublicKeyCredentialDescriptor objects, indicating acceptable public key credentials to the Relying Party (RP). Its significance lies in:

• Selective Authentication: Directs the authenticator to use specific credentials
• Credential Preferences: Credentials are listed in descending order of preference, guiding the client in selection.
• Enhanced User Experience: Streamlines the authentication process by guiding the client on which credentials to use, reducing user input.

---

The allowCredentials field in WebAuthn plays a pivotal role in defining a secure and efficient authentication flow. By specifying which credentials are acceptable, it ensures that the authentication process is both secure and user-friendly.

• User-Centric Authentication: Tailors the authentication process to individual users by allowing the selection of specific credentials.
• Role in Authentication Flow: Informs the client (such as a browser or mobile app) which credentials are acceptable, particularly important when the user has multiple credentials registered.
• Technical Implementation: For developers, understanding how allowCredentials influences the authentication flow is crucial for building robust WebAuthn implementations.

---

allowCredentials specifies which registered credentials can be used for user authentication, guiding the client in the authentication process.

It enhances security by specifying exact credentials for authentication, and improves user experience by streamlining the credential selection process.

Without an allowCredentials list, the client may not know which specific credential to use, leading to additional user interaction to select the appropriate credential.