function finish(err) {
	      callback(err, err ? null : self.token);
	    }
Loads token from the configuration object. This is used internally
by the SDK to ensure that refreshable {Token} objects are properly
refreshed and loaded when sending a request. If you want to ensure that
your token is loaded prior to a request, you can use this method
directly to provide accurate token data stored in the object.

@note If you configure the SDK with static token, the token data should
  already be present in {token} attribute. This method is primarily necessary
  to load token from asynchronous sources, or sources that can refresh
  token periodically.
@example Getting your access token
  AWS.config.getToken(function(err) {
    if (err) console.log(err.stack); // token not loaded
    else console.log("Token:", AWS.config.token.token);
  })
@callback callback function(err)
  Called when the {token} have been properly set on the configuration object.

  @param err [Error] if this is set, token was not successfully loaded and
    this error provides information why.
@see token