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diff --git a/shareguard-authnz-external.hs b/shareguard-authnz-external.hs
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+{-
+shareguard-authnz-external: mod_authnz_external-to-ShareGuard interface
+
+  Copyright (C) 2011  Clint Adams <clint@gnu.org>
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU Affero General Public License as
+  published by the Free Software Foundation, either version 3 of the
+  License, or (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU Affero General Public License for more details.
+
+  You should have received a copy of the GNU Affero General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+-}
+
+import System.Exit ( exitWith, ExitCode (..) )
+import System.Environment
+import System.IO.Error
+
+import Control.Monad.Trans
+import Control.Monad.Error
+
+import System.Path.NameManip (normalise_path, guess_dotdot, slice_path)
+
+import Config as C
+import DB as D
+
+data AuthQuery = AuthQuery { uname :: String  
+			, pass :: String  
+			, uri :: String
+			}
+main = do
+	uri <- catch (getEnv "URI") envvarHandler
+	cnf <- C.getConfig "/usr/local/etc/shareguard.conf"
+	user <- getLine  
+	pw <- getLine
+	passwords <- D.withDB cnf $ \db -> getUserPw db
+	let dbpass = snd $ head $ filter ((==user).fst) passwords
+	alldirs <- D.withDB cnf $ \db -> getUserDirs db
+	let dirs = map snd (filter ((==user).fst) alldirs)
+	if isValidRequest (AuthQuery user pw uri) dbpass dirs
+		then exitWith (ExitSuccess)
+		else exitWith (ExitFailure 1)
+
+envvarHandler :: IOError -> IO (String)  
+envvarHandler e
+    | isDoesNotExistError e = return ""
+    | otherwise = ioError e
+
+isValidRequest :: AuthQuery -> String -> [String] -> Bool
+isValidRequest (AuthQuery {uname = u, pass = p, uri = req}) dbpass dirs =
+	and [isCorrectPassword p dbpass,
+		isAuthorizedURI (rootDir $ sanitizeURI req) dirs]
+
+isCorrectPassword :: String -> String -> Bool
+isCorrectPassword p1 p2 =
+	and [p1 == p2, p2 /= ""]
+
+isAuthorizedURI :: Maybe String -> [String] -> Bool
+isAuthorizedURI Nothing _ = False
+isAuthorizedURI (Just req) dirs =
+	elem req dirs
+
+rootDir :: Maybe String -> Maybe String
+rootDir Nothing = Nothing
+rootDir (Just x) = Just (head (slice_path x))
+
+sanitizeURI :: String -> Maybe String
+sanitizeURI uri =
+	guess_dotdot (normalise_path uri)