Added the ability to pass credentials when creating client storages.

This is experimental in that passing credentials will cause
connections to an ordinary ZEO server to fail, but it facilitates
experimentation with custom ZEO servers. Doing this with custom ZEO
clients would have been awkward due to the many levels of
composition involved.

In the future, we expect to support server security plugins that
consume credentials for authentication (typically over SSL).

Note that credentials are opaque to ZEO. They can be any object with
a true value.  The client mearly passes them to the server, which
will someday pass them to a plugin.

CHANGES.rst

 Changelog
 =========
 
+- Added the ability to pass credentials when creating client storages.
+
+  This is experimental in that passing credentials will cause
+  connections to an ordinary ZEO server to fail, but it facilitates
+  experimentation with custom ZEO servers. Doing this with custom ZEO
+  clients would have been awkward due to the many levels of
+  composition involved.
+
+  In the future, we expect to support server security plugins that
+  consume credentials for authentication (typically over SSL).
+
+  Note that credentials are opaque to ZEO. They can be any object with
+  a true value.  The client mearly passes them to the server, which
+  will someday pass them to a plugin.
 
 5.0.0a1 (2016-07-21)
 --------------------

src/ZEO/ClientStorage.py

@@ -99,6 +99,7 @@ class ClientStorage(ZODB.ConflictResolution.ConflictResolvingStorage):
                  wait=True,
                  drop_cache_rather_verify=True,
                  username=None, password=None, realm=None,
+                 credentials=None,
                  # For tests:
                  _client_factory=ZEO.asyncio.client.ClientThread,
                  ):
@@ -261,6 +262,7 @@ class ClientStorage(ZODB.ConflictResolution.ConflictResolvingStorage):
             ZEO.asyncio.client.Fallback if read_only_fallback else read_only,
             wait_timeout or 30,
             ssl = ssl, ssl_server_hostname=ssl_server_hostname,
+            credentials=credentials,
             )
         self._call = self._server.call
         self._async = self._server.async

src/ZEO/asyncio/client.py

@@ -73,7 +73,8 @@ class Protocol(base.Protocol):
 
     def __init__(self, loop,
                  addr, client, storage_key, read_only, connect_poll=1,
-                 heartbeat_interval=60, ssl=None, ssl_server_hostname=None):
+                 heartbeat_interval=60, ssl=None, ssl_server_hostname=None,
+                 credentials=None):
         """Create a client interface
 
         addr is either a host,port tuple or a string file name.
@@ -93,6 +94,7 @@ class Protocol(base.Protocol):
         self.futures = {} # { message_id -> future }
         self.ssl = ssl
         self.ssl_server_hostname = ssl_server_hostname
+        self.credentials = credentials
 
         self.connect()
 
@@ -178,17 +180,19 @@ class Protocol(base.Protocol):
 
         self._write(self.protocol_version)
 
+        credentials = (self.credentials,) if self.credentials else ()
+
         try:
             try:
                 server_tid = yield self.fut(
                     'register', self.storage_key,
                     self.read_only if self.read_only is not Fallback else False,
-                    )
+                    *credentials)
             except ZODB.POSException.ReadOnlyError:
                 if self.read_only is Fallback:
                     self.read_only = True
                     server_tid = yield self.fut(
-                        'register', self.storage_key, True)
+                        'register', self.storage_key, True, *credentials)
                 else:
                     raise
             else:
@@ -284,7 +288,7 @@ class Client(object):
     def __init__(self, loop,
                  addrs, client, cache, storage_key, read_only, connect_poll,
                  register_failed_poll=9,
-                 ssl=None, ssl_server_hostname=None):
+                 ssl=None, ssl_server_hostname=None, credentials=None):
         """Create a client interface
 
         addr is either a host,port tuple or a string file name.
@@ -302,6 +306,7 @@ class Client(object):
         self.client = client
         self.ssl = ssl
         self.ssl_server_hostname = ssl_server_hostname
+        self.credentials = credentials
         for name in Protocol.client_delegated:
             setattr(self, name, getattr(client, name))
         self.cache = cache
@@ -367,6 +372,7 @@ class Client(object):
                          self.storage_key, self.read_only, self.connect_poll,
                          ssl=self.ssl,
                          ssl_server_hostname=self.ssl_server_hostname,
+                         credentials=self.credentials,
                          )
                 for addr in self.addrs
                 ]
@@ -730,10 +736,12 @@ class ClientThread(ClientRunner):
 
     def __init__(self, addrs, client, cache,
                  storage_key='1', read_only=False, timeout=30,
-                 disconnect_poll=1, ssl=None, ssl_server_hostname=None):
+                 disconnect_poll=1, ssl=None, ssl_server_hostname=None,
+                 credentials=None):
         self.set_options(addrs, client, cache, storage_key, read_only,
                          timeout, disconnect_poll,
-                         ssl=ssl, ssl_server_hostname=ssl_server_hostname)
+                         ssl=ssl, ssl_server_hostname=ssl_server_hostname,
+                         credentials=credentials)
         self.thread = threading.Thread(
             target=self.run,
             name="%s zeo client networking thread" % client.__name__,