Update for authentication and for a few tools.

doc/ZEO/howto.txt

@@ -164,6 +164,30 @@ http://www.zope.com/Products/ZopeProducts/ZRS.  In general, it could
 be used to with a system that arranges to provide hot backups of
 servers in the case of failure.
 
+Authentication
+~~~~~~~~~~~~~~
+
+ZEO supports optional authentication of client and server using a
+password scheme similar to HTTP digest authentication (RFC 2069).  It
+is a simple challenge-response protocol that does not send passwords
+in the clear, but does not offer strong security.  The RFC discusses
+many of the limitations of this kind of protocol.  Note that this
+feature provides authentication only.  It does not provide encryption
+or confidentiality.
+
+The challenge-response also produces a session key that is used to
+generate message authentication codes for each ZEO message.  This
+should prevent session hijacking.
+
+Guard the password database as if it contained plaintext passwords.
+It stores the hash of a username and password.  This does not expose
+the plaintext password, but it is sensitive nonetheless.  An attacker
+with the hash can impersonate the real user.  This is a limitation of
+the simple digest scheme.
+
+The authentication framework allows third-party developers to provide
+new authentication modules.
+
 Installing software
 -------------------
 
@@ -282,6 +306,19 @@ transaction-timeout
         transaction takes too long, the client connection will be closed
         and the transaction aborted.
 
+authentication-protocol
+        The name of the protocol used for authentication.  The
+        only protocol provided with ZEO is "digest," but extensions
+        may provide other protocols.
+
+authentication-database
+        The path of the database containing authentication credentials.
+
+authentication-realm
+        The authentication realm of the server.  Some authentication
+        schemes use a realm to identify the logic set of usernames
+        that are accepted by this server.
+
 Configuring client
 ------------------
 
@@ -354,6 +391,10 @@ read-only-fallback
         acceptable as a fallback when no writable storages are
         available.  Defaults to false.  At most one of read_only and
         read_only_fallback should be true.
+realm
+        The authentication realm of the server.  Some authentication
+        schemes use a realm to identify the logic set of usernames
+        that are accepted by this server.
 
 A ZEO client can also be created by calling the ClientStorage
 constructor explicitly.  For example::
@@ -384,6 +425,15 @@ server.  The server will continue writing to the renamed log file
 until it receives the signal.  After it receives the signal, the
 server will create a new file with the old name and write to it.
 
+Tools
+-----
+
+There are a few scripts that may help running a ZEO server.  The
+zeopack.py script connects to a server and packs the storage.  It can
+be run as a cron job.  The zeoup.py script attempts to connect to a
+ZEO server and verify that is is functioning.  The zeopasswd.py script
+manages a ZEO servers password database.
+
 Diagnosing problems
 -------------------