IBM Lotus Notes SIGNING XPAGES DOCUMENT in WEB browser

First of all. I am a beginner in IBM development and i don't have a lot of experience in IBM Domino server or Xpages.

My task is like this: "Create a document using xpages, and sign document using ID from server ID Vault and get Verified by server".

I have a simple form consisting of two inputs (subject, content). I have Xpages page and everything set up for creating and viewing documents. But i got stuck trying to sign each document with user id. I have set up user ID in Vault. Then I enter X-page from browser (not Notes Client) i have access to forms and documents.. with configured credentials.

So basically what I'm asking is:

HOW TO SIGN DOCUMENTS from web browser (X-pages) using ID from Vault and get Verified by Server ?