diff -urN mldonkey/src/daemon/common/commonOptions.ml mldonkey_with_authpatch/src/daemon/common/commonOptions.ml
--- mldonkey/src/daemon/common/commonOptions.ml	2007-04-23 00:31:53.000000000 +0200
+++ mldonkey_with_authpatch/src/daemon/common/commonOptions.ml	2007-04-26 18:56:37.000000000 +0200
@@ -1363,7 +1358,26 @@
   "Regexp of comments to filter out, example: string1|string2|string3"
     string_option "http://|https://|www\\."
 
+let auth_cmd = define_option current_section ["auth_cmd"]
+  "A command that is called when authorizing a user (i.e. on startup and
+  on auth command. The following environment variables are set:
+    $USERNAME - the username
+    $PASSWORD - the users password
+  
+  The command should return a value indicating if the authentication
+  is successful:
+    0 - The authentication is immidiately accepted IF the user exists
+    1 - The authentication is immidiately rejected
+    2 - An addition check against the MD4 has is performed.
+  
+  If the user does not exist in the internal database, the authentication
+  will fail, also when the program returns 0.
+  
+  If this value is not set, a normal authentication against the internal
+  database is performed.
+  If this option is set and there is an error running the command the
+  authentication will fail."
+    string_option ""
 
 
 (*************************************************************************)
diff -urN mldonkey/src/daemon/common/commonUserDb.ml mldonkey_with_authpatch/src/daemon/common/commonUserDb.ml
--- mldonkey/src/daemon/common/commonUserDb.ml	2006-11-09 22:32:26.000000000 +0100
+++ mldonkey_with_authpatch/src/daemon/common/commonUserDb.ml	2007-04-26 19:04:41.177275304 +0200
@@ -313,9 +313,32 @@
 let user2_user_set_password user pass_string =
   user.user_pass <- Md4.string pass_string
 
-let valid_password user pass =
+let valid_password user pass = 
   try
-    user2_user_password user = Md4.string pass
+    if !!auth_cmd <> "" && user2_user_exists user
+    then
+      try
+        let pid = Unix.create_process_env !!auth_cmd
+          [|""|]
+          (Array.of_list (Printf.sprintf "USERNAME=%s" user :: Printf.sprintf "PASSWORD=%s" pass :: []))
+          Unix.stdin Unix.stdout Unix.stderr in
+
+        let _pid, status = Unix.waitpid [] pid in
+        match status with
+          | Unix.WEXITED exitcode -> 
+            (match exitcode with
+	      | 0 -> true
+	      | 1 -> false
+	      | _ -> user2_user_password user = Md4.string pass
+	    )
+          | Unix.WSIGNALED signal -> false
+          | Unix.WSTOPPED signal -> false
+      with Unix.Unix_error (code, f, arg) -> false
+      (*
+      Printf.sprintf "%s failed%s: %s" f (if arg = "" then "" else " on " ^ arg) (Unix.error_message code)
+      *)
+    else
+      user2_user_password user = Md4.string pass
   with Not_found -> false
 
 let has_empty_password user =