Matt's Headroom

Controlling the Name Displayed During WebAuthn Registration (and Authentication)

- 3 minute read

WebAuthn defines two possible values that Relying Parties can set to help users understand for which account they’re registering a credential and using in subsequent authentications:

It was unclear to me from reading the spec how exactly I was supposed to use either value:

user.name

When inherited by PublicKeyCredentialUserEntity, it is a human-palatable identifier for a user account. It is intended only for display, i.e., aiding the user in determining the difference between user accounts with similar displayNames. For example, “alexm”, “[email protected]” or “+14255551234”.

user.displayName

A human-palatable name for the user account, intended only for display. For example, “Alex Müller” or “田中倫”. The Relying Party SHOULD let the user choose this, and SHOULD NOT restrict the choice more than necessary.

Practically speaking, it seemed easy for an RP to misconfigure these values and get users into a state in which it’s difficult to know, for example, which environment/deployment/etc… a particular passkey was good for:

Chrome

Chrome displaying a list of WebAuthn credentials. All have the same RP ID, while two have the username “mmiller” and the third uses my entire email address

1Password

1Password displaying three seemingly identical passkeys for their fake PassParcel demo site

Safari

Safari displaying five passkeys, all showing the same usernames across two RP IDs

Which credentials are still valid? Which can I delete? From these real-world examples it seems impossible to tell.

I decided to attempt registration across the most common platforms and browsers and record which of these two values made it into UI that users actually see. I was also curious to see which of the values appeared in credential management UI. In the end I hoped to understand how I might better leverage these values to help users manage their passkey collections.

## Chrome M109 (macOS 13.2)

Chrome used user.name for both registration and passkey management.

Registration:

The Chrome registration prompt displays the value of user.name

Management:

The Chrome management UI displays user.name

## Safari 16.3 (macOS 13.2)

Safari also used only user.name for registration and passkey management.

Registration:

The Safari registration prompt displays the value of user.name

Management:

The Safari management UI displays user.name

## Windows Hello (Windows 11 21H2)

Windows Hello solely used user.name.

Registration:

The Windows Hello registration prompt displays the value of user.name

Management:

N/A

NOTE: I couldn’t find passkeys management in Chrome on Windows, but I’ve been informed I need to be on Windows 11 22H2 to see it. I’m updating now and will update this section when I can grab a screenshot (it’ll probably look like macOS Chrome above)

## iOS 16.3

iOS too limited itself to using user.name for registration and management.

Registration:

The iOS registration prompt displays the value of user.name

Management:

The iOS management UI displays user.name

## Android 13

Android was the only platform that leveraged both user.name and user.displayName.

Registration:

The Android registration prompt displays the value of user.displayName above user.name

Management:

The Android management UI displays user.name

## Conclusion

Based on what I observed today it appears that user.name is an RP’s best option for differentiating credentials that use the same username but only work for specific environments/deployments/etc…

(BTW I submitted a GitHub issue to the WebAuthn spec related to differentiating credentials via a new “note” value in registration options. Based on what I’m seeing above, though, I can agree with Yubico’s John Bradley that there’s an opportunity for clients and platforms to also leverage user.displayName instead of adding anything new.)