The World Wide Web Consortium (W3C), the body responsible for web standards, has published a working draft of an API designed to improve the security of web apps.
It will therefore enable web applications to check a user's identity in more secure ways than are currently possible between browsers and HTTP servers.
Uses for the API include user or service authentication, document or code signing, and the confidentiality and integrity of communications. You can also use the API to think up ad-hoc applications of cryptography within your own apps.
The W3C Web Cryptography Working Group is looking for feedback on:
developer convenience for managing keys and algorithms;
comments on open issues the WG is currently dealing with, highlighted in this working draft;
potential missing functionalities to deploy secure web applications.