curl --request POST \
  --url https://api.dfns.io/auth/registration/delegated \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --header 'X-DFNS-USERACTION: <api-key>' \
  --data '
{
  "email": "<string>",
  "externalId": "<string>"
}
'

{
  "user": {
    "id": "<string>",
    "displayName": "<string>",
    "name": "<string>"
  },
  "temporaryAuthenticationToken": "<string>",
  "challenge": "<string>",
  "supportedCredentialKinds": {
    "firstFactor": [],
    "secondFactor": []
  },
  "authenticatorSelection": {
    "requireResidentKey": true
  },
  "pubKeyCredParams": [
    {
      "alg": 123
    }
  ],
  "excludeCredentials": [
    {
      "id": "cr-6uunn-bm6ja-f6rmod5kqrk5rbel"
    }
  ],
  "otpUrl": "<string>",
  "rp": {
    "id": "<string>",
    "name": "<string>"
  }
}