New fields in clientDataJSON

[apowers313]

clientDataJson in Chrome Canary Version 68.0.3438.3 now has a hashAlgorithm property. Should use this field if it is present.

{
"rawClientDataJson":"{\"challenge\":\"ICFGoPRC4FMPIKSX5cexUVwBzEX5H9KWnRYQZVCiGpesn59PzizxgLYQS_QRIy-TBYsRg1_zJ4hLpTNLeLUFiA\",\"clientExtensions\":{},\"hashAlgorithm\":\"SHA-256\",\"origin\":\"https://localhost:8443\",\"type\":\"webauthn.create\"}",
}