DavServlet modifications from Rutgers

/**
	 * Setup and cleanup around this request.
	 * @param req HttpServletRequest object with the client request
	 * @param res HttpServletResponse object back to the client
	 */
	protected void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, java.io.IOException
	{
		SakaidavServletInfo info = newInfo(req);

		// RequestFilter will give us any session with this username,
		// even if there's no cookie (which will normally be the case)
		// Thus we can't assume that just because there's a session,
		// we're authenticated. So we always check. In theory if we
		// can verify that this is a proper cookie-based session
		// we could skip the test. Note that there's nothing in the
		// DAV RFC about cookies, so it's actually non-standard to
		// use them, and I think most clients don't.
		// See kernel/request/src/java/org/sakaiproject/util/RequestFilter.java

		Session session = SessionManager.getCurrentSession();

		// try to authenticate based on a Principal (one of ours) in the req
		Principal prin = req.getUserPrincipal();

		if ((prin != null) && (prin instanceof DavPrincipal))
		    {
			String eid = prin.getName();
			String pw = ((DavPrincipal) prin).getPassword();
			Evidence e = new IdPwEvidence(eid, pw);
			
			// authenticate
			try
			    {
				if ((eid.length() == 0) || (pw.length() == 0))
				    {
					throw new AuthenticationException("missing required fields");
				    }
				
				Authentication a = AuthenticationManager.authenticate(e);
				
				// login the user if needed. RequestFilter
				// may have found a session with the right 
				// userid. If so there's no need for a login
				// as long as it's the right userid. 
				// getUserID could be our id, null, or the
				// wrong one. The wrong one should be rare.

				if (session.getUserId() != eid)
				    LoginUtil.login(a, req);
			    }
			catch (AuthenticationException ex)
			    {
				// not authenticated
				res.sendError(401);
				return;
			    }
		    } 
		else
		    {
			// user name missing, so can't authenticate
			res.sendError(401);
			return;
		    }

// Setup... ?

		try
		{
			doDispatch(info, req, res);
		}
		finally
		{
			log(req, info);
		}
	}