Support reading extra_attributes

[ghost]

A CAS server may pass extra_attributes (like full name) for the user being logged in. Looks like currently there is no way for this client to read that.

Is that correct?

[ghost]

@serac @scottt732 Any thoughts on this?

[ghost]

For example other CAS libraries, like the standard Ruby one would do this.

[ghost]

More specifically the cas:attributes.

If the library doesn't parse it, is there a handle to the POST body XML somewhere so that the client app can parse it themselves.

[serac]

The recommended way to consume attributes is via the SAML 1.1 protocol, which this client (and many others) supports. See http://jasig.github.io/cas/4.2.x/protocol/SAML-Protocol.html.