Consider whether BrokerSpec.AuthSecret should change

[pmorie]

Currently the OSB API only supports basic auth. Adding an OAuth flow is being discussed, and so we should assume that long-term, there will be multiple forms of auth. Currently, we have a single field called AuthSecret in the BrokerSpec type, so the type of auth being used does not surface at all in the API. I think we should consider using a union type to make explicit in the broker spec what form of auth is requested. Example:

type BrokerSpec struct {
  // other fields omitted

  AuthInfo *AuthInfo
}

type AuthInfo struct {
  BasicAuthSecret *v1.ObjectReference

  // in the future:
  OAuthSecret *v1.ObjectReference
}

...this would allow us to add new auth methods in a backward-compatible way.

Thoughts?