PublicKeyCredential: parseCreationOptionsFromJSON() static method

options

An object with the same structure as a PublicKeyCredentialCreationOptions, but with base64url-encoded strings used in place of buffer properties.

A PublicKeyCredentialCreationOptions object.

EncodingError DOMException

Thrown the options object cannot be converted into a PublicKeyCredentialCreationOptions object.

The Web Authentication process for creating a key pair and registering a user involves a relying party server sending the web app information needed to create a credential, including details about the user identity, the relying party, and a "challenge". The web app passes this information to an authenticator to create the credential, by calling navigator.credentials.create() with a PublicKeyCredentialCreationOptions object as an argument.

The specification does not define how the information needed for creating a credential is sent. A convenient approach is for the server to encapsulate the information in a JSON type representation of the PublicKeyCredentialCreationOptions object that mirrors its structure but encodes buffer properties such as the challenge and user.id as base64url strings. This object can be serialized to a JSON string, sent to the web app and deserialized, and then converted to a PublicKeyCredentialCreationOptions object using parseCreationOptionsFromJSON().

When registering a new user, a relying party server will supply information about the expected credentials to the web app. The code below defines this information in the form described in the options parameter above (taken from the "getting an AuthenticatorAttestationResponse" in AuthenticatorResponse):

const createCredentialOptionsJSON = {
  challenge:
    "21, 31, 105, " /* 29 more random bytes generated by the server in this string */,
  rp: {
    name: "Example CORP",
    id: "login.example.com",
  },
  user: {
    id: "16",
    name: "canand@example.com",
    displayName: "Carina Anand",
  },
  pubKeyCredParams: [
    {
      type: "public-key",
      alg: -7,
    },
  ],
};

Because this object only uses JSON data types, it can be serialized to JSON using JSON.stringify() and sent to the web app.

JSON.stringify(createCredentialOptionsJSON);

The web app can deserialize the JSON string back to a createCredentialOptionsJSON object (not shown). The parseCreationOptionsFromJSON() method is used to convert that object to the form that can be used in navigator.credentials.create():

// Convert options to form used by create()
const createCredentialOptions =
  PublicKeyCredential.parseCreationOptionsFromJSON(
    createCredentialOptionsJSON, // JSON-type representation
  );

navigator.credentials
  .create({ createCredentialOptions })
  .then((newCredentialInfo) => {
    // Handle the new credential information here.
  })
  .catch((err) => {
    console.error(err);
  });

• Web Authentication API
• PublicKeyCredential.parseRequestOptionsFromJSON()
• PublicKeyCredential.toJSON()