Gap in the readme, how do I sign an object with the Signature property?

[sir-farfan]

The Usages says

Include the types.Signature struct from this package in your application messages

proceeds to create the AppHdr struct which is never used or referenced again, LOL.

I need to sign Response and Assertion objects from for post binding, I got an starting base by copying them from gosaml2 and adding the Signature property.

How do I get from embedding the Signature struct to actually signing the objects?