[tahoe-dev] webapi is vulnerable to XSRF attacks. (Defect #98)

[Nathan]

I've added a ticket discussing how the webapi is vulnerable to XSRF attacks:
http://allmydata.org/trac/tahoe/ticket/98

Because this is a little known prototype, I categorized it as minor.
However, if we plan on Tahoe becoming popular, I believe it should be
addressed.  The sooner, the better because of backwards compatibility
issues.

I believe this should be fairly easy to fix technically but would
require altering the webapi and web user interface.

The largest interface change for the solution I imagine is to prevent
URLs from initiating actions unless they include a session-specific
unguessable nonce.  This means users can't cut'n'paste URLs to/from
eachother to share data.  A workaround is to allow them to paste in a
constrained input form provided by the web UI, but even this needs to
be carefully thought out.

I'd like to implement a solution if we agree on the UI changes.

Regards,
Nathan