Perform the Access Token phase of OAuth, invoking
function (defaulting to "access_token" if
function is NULL).
verifier is only used if you are using OAuth 1.0a. This is either the "oauth_verifier" parameter that was passed to your callback
URI, or a string that the user enters in some other manner (for example in a popup dialog) if "oob" was passed to
request_token. For OAuth 1.0, pass
This method will return once the method has been queued,
callback will be invoked when it has completed.
the function name to invoke
a OAuthProxyAuthCallback to invoke on completion
Object to weakly reference and tie the lifecycle of the method call too
user data to pass to