Non repudiation means that if a users sign the document. For him is impossible to say that he didn't sign that document. It should be equivalent to handwritten signature. see-here-for-more-info
Note that the problem is more of a legal than technical/implementation issue. Your links above to the FDA regulations and the other stackoverflow question How to achieve non-repudiation? emphasizes the legal aspect of it as well.
That means you will need to ensure compliance to laws of each country (e.g. ESIGN Act in the US). What is interesting about ESIGN is that it preserves the right of a person to NOT use electronic signatures. Might I suggest using a service such as https://www.docusign.com/ instead - see its section on legality.