The SAML 2.0 Debugger allows you to encode and decode SAML messages.
How to use it?
To grab the raw URLs and post data from the browser when you login, I reccomend to use the httpLiveHeaders add-on to Firefox.
Here is a demo video explaining how to use:
Note: The SAML 2.0 debugger is implemented as a module in simpleSAMLphp. That means if you run simpleSAMLphp, you can simply enable it and run it on your own host.