Documentation on how to generate values for context

[sbastn]

Hello,

We're trying out your library and we're running into issues when generating values to build a context object. Specifically, any documentation on how to generate the following values would be great:

• client_data_json
• challenge

Could we help you document this in the Readme?

We're currently stuck at this step:

    challenge = 'random-string-generated-by-rp-server'

    client_data_json = Base64.urlsafe_encode64({
      type: "webauthn.create",
      challenge: challenge,
      origin: request.base_url,
    }.to_json, padding: false)
    
    context = WebAuthn.context_for(
      client_data_json, # NOTE: URL-safe Base64 encoded
      origin: request.base_url,
      challenge: challenge
    )

This fails with Invalid Challenge. We're testing this in localhost, do we need https for the origin to be valid?

Thanks in advance.