How Webhook Token Authentication Works

// Code from https://github.com/kubernetes/kubernetes/blob/master/staging/src/k8s.io/apiserver/pkg/authentication/request/union/union.go#L34-L71
// New() returns a request authenticator that validates credentials using a chain of authenticator.Request objects.
// The entire chain is tried until one succeeds. If all fail, an aggregate error is returned.
func New(authRequestHandlers ...authenticator.Request) authenticator.Request {
	if len(authRequestHandlers) == 1 {
		return authRequestHandlers[0]
	}
	return &unionAuthRequestHandler{Handlers: authRequestHandlers, FailOnError: false}
}
// NewFailOnError() returns a request authenticator that validates credentials using a chain of authenticator.Request objects.
// The first error short-circuits the chain.
func NewFailOnError(authRequestHandlers ...authenticator.Request) authenticator.Request {
	if len(authRequestHandlers) == 1 {
		return authRequestHandlers[0]
	}
	return &unionAuthRequestHandler{Handlers: authRequestHandlers, FailOnError: true}
}
// AuthenticateRequest authenticates the request using a chain of authenticator.Request objects.
func (authHandler *unionAuthRequestHandler) AuthenticateRequest(req *http.Request) (*authenticator.Response, bool, error) {
	var errlist []error
	for _, currAuthRequestHandler := range authHandler.Handlers {
		resp, ok, err := currAuthRequestHandler.AuthenticateRequest(req)
		if err != nil {
			if authHandler.FailOnError {
				return resp, ok, err
			}
			errlist = append(errlist, err)
			continue
		}
		if ok {
			return resp, ok, err
		}
	}
	return nil, false, utilerrors.NewAggregate(errlist)
}