I'm building a web application that builds a XML document based on the user input. After the doc is created, it needs to follow an approval path, e.g. a workflow, where several users "sign" the document. The signature from the user point of view is just checking a field and clickin "accept", but what I need is for the document to be digitally signed in each step, to finally store it signed in a database.
What kind of devices/tools do I need to use? X.509 certificates on the client browser? Public/Private keys generated by the app? Any link to documentation will be appreciated.