Auth for playground

[eyurtsev]

Changes on the UI required:

• when security scheme is specified:

  • all information except for security scheme are removed from window
    constants
  • after successful auth, UI needs to make web-request to appropriate
    endpoints to get configuration information using auth.

• If no security scheme is specified, then we can dump all the information in
  the window (but that's just an optimization I think easier to make a single
  code path that makes all the relevant network requests to collect the config
  info)

More backend changes required:

• Add any missing endpoints to collect config information that's hard-coded
  into the index.html file as global constants.
• Spec out changes required to special-case playground dependencies