[Ur] Announcing an OpenID library

[Adam Chlipala]

I've posted a public Mercurial repo for an OpenID relying party library:
     http://hg.impredicative.com/openid
As is often the case, this library requires the latest version of Ur/Web 
from its public repo.

Quick primer on what the first line of this message means:
OpenID is an increasingly popular protocol for distributed 
authentication.  With this library, users can log into your application 
with their passwords for Google, Yahoo!, and many other participating 
providers.  Even better, they can do so without having to tell you their 
passwords; instead, the provider sends your app guarantees about who is 
who.  The whole process is suitably crypto-ized such that you can trust 
that identity providers are really making the claims your app is told 
that they are making.

There is a test application in tests/test.urp.  The library 
documentation is in the form of comments in src/ur/openid.urs.

P.S.: I noticed that, the last time I announced repos for separate 
libraries, someone added them to a wiki page about libraries and FFI 
bindings.  I have no problem with that, of course, but I'm also linking 
to libraries from the main (static) Ur page.  I hope that I'll have the 
opportunity eventually to add links to other libraries that have my 
personal blessing.  For now, none of the others from the wiki page pass 
that bar for me, since they allow very bad interactions with Ur/Web 
transactions.