class Signet::OAuth2::Client

hash with the fetched authentication token.
This reopens Client to add #apply and #apply! methods which update a
Signet::OAuth2::Client creates an OAuth2 client

def apply(a_hash, opts = {})

Returns a clone of a_hash updated with the authentication token 
def apply(a_hash, opts = {})
  a_copy = a_hash.clone
  apply!(a_copy, opts)
  a_copy
end

def apply!(a_hash, opts = {})

Updates a_hash updated with the authentication token 
def apply!(a_hash, opts = {})
  # fetch the access token there is currently not one, or if the client
  # has expired
  fetch_access_token!(opts) if access_token.nil? || expires_within?(60)
  a_hash[AUTH_METADATA_KEY] = "Bearer #{access_token}"
end

def fetch_access_token!(options = {}) 

def fetch_access_token!(options = {})
  info = orig_fetch_access_token!(options)
  notify_refresh_listeners
  info
end

def notify_refresh_listeners 

def notify_refresh_listeners
  listeners = @refresh_listeners || []
  listeners.each do |block|
    block.call(self)
  end
end

def on_refresh(&block) 

def on_refresh(&block)
  @refresh_listeners ||= []
  @refresh_listeners << block
end

def updater_proc

a closure
Returns a reference to the #apply method, suitable for passing as 
def updater_proc
  lambda(&method(:apply))
end