p2phttp: Allow unauthenticated users to lock content by default

* p2phttp: Allow unauthenticated users to lock content by default.
* p2phttp: Added --unauth-nolocking option to prevent unauthenticated
  users from locking content.

The rationalle for this is that locking is not really a write operation, so
makes sense to allow in a repository that only allows read-only access. Not
supporting locking in that situation will prevent the user from dropping
content from a special remote they control in cases where the other copy of
the content is on the p2phttp server.

Also, when p2phttp is configured to also allow authenticated access,
lockcontent was resulting in a password prompt for users who had no way to
authenticate. And there is no good way to distinguish between the two types
of users client side.

--unauth-nolocking anticipates that this might be abused, and seems better
than disabling unauthenticated access entirely if a server is being
attacked. It may be that rate limiting locking by IP address or similar
would be an effective measure in such a situation. Or just limiting the
number of locks by anonymous users that can be live at any one time. Since
the impact of such an DOS attempt is limited to preventing dropping content
from the server, it seems not a very appealing target anyway.

Command/P2PHttp.hs

@@ -40,6 +40,7 @@ data Options = Options
 	, authEnvHttpOption :: Bool
 	, unauthReadOnlyOption :: Bool
 	, unauthAppendOnlyOption :: Bool
+	, unauthNoLockingOption :: Bool
 	, wideOpenOption :: Bool
 	, proxyConnectionsOption :: Maybe Integer
 	, clusterJobsOption :: Maybe Int
@@ -83,6 +84,10 @@ optParser _ = Options
 		( long "unauth-appendonly"
 		<> help "allow unauthenticated users to read and append to the repository"
 		)
+	<*> switch
+		( long "unauth-nolocking"
+		<> help "prevent unauthenticated users from locking content in the repository"
+		)
 	<*> switch
 		( long "wideopen"
 		<> help "give unauthenticated users full read+write access"
@@ -128,15 +133,25 @@ seek o = getAnnexWorkerPool $ \workerpool ->
 
 mkGetServerMode :: M.Map Auth P2P.ServerMode -> Options -> GetServerMode
 mkGetServerMode _ o _ Nothing
-	| wideOpenOption o =
-		ServerMode P2P.ServeReadWrite False
-	| unauthAppendOnlyOption o =
-		ServerMode P2P.ServeAppendOnly canauth
-	| unauthReadOnlyOption o =
-		ServerMode P2P.ServeReadOnly canauth
+	| wideOpenOption o = ServerMode
+		{ serverMode = P2P.ServeReadWrite
+		, unauthenticatedLockingAllowed = unauthlock
+		, authenticationAllowed = False 
+		}
+	| unauthAppendOnlyOption o = ServerMode 
+		{ serverMode = P2P.ServeAppendOnly
+		, unauthenticatedLockingAllowed = unauthlock
+		, authenticationAllowed = canauth
+		}
+	| unauthReadOnlyOption o = ServerMode
+		{ serverMode = P2P.ServeReadOnly
+		, unauthenticatedLockingAllowed = unauthlock
+		, authenticationAllowed = canauth
+		}
 	| otherwise = CannotServeRequests
   where
 	canauth = authEnvOption o || authEnvHttpOption o
+	unauthlock = not (unauthNoLockingOption o)
 mkGetServerMode authenv o issecure (Just auth) =
 	case (issecure, authEnvOption o, authEnvHttpOption o) of
 		(Secure, True, _) -> checkauth
@@ -144,7 +159,11 @@ mkGetServerMode authenv o issecure (Just auth) =
 		_ -> noauth
   where
 	checkauth = case M.lookup auth authenv of
-		Just servermode -> ServerMode servermode False
+		Just servermode -> ServerMode 
+			{ serverMode = servermode
+			, authenticationAllowed = False
+			, unauthenticatedLockingAllowed = False
+			}
 		Nothing -> noauth
 	noauth = mkGetServerMode authenv noautho issecure Nothing
 	noautho = o { authEnvOption = False, authEnvHttpOption = False }