gitweb: Add a per-repository authorization hook.

Add a configuration variable that can be used to specify an
arbitrary subroutine that will be called in the same situations
where $export_ok is checked, and its return value used
to decide whether the repository is to be shown.

This allows the user to implement custom authentication
schemes, for example by issuing a subrequest through mod_perl
and checking if Apache will authorize it.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Acked-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/INSTALL

@@ -166,6 +166,27 @@ Gitweb repositories
   shows repositories only if this file exists in its object database
   (if directory has the magic file named $export_ok).
 
+- Finally, it is possible to specify an arbitrary perl subroutine that
+  will be called for each project to determine if it can be exported.
+  The subroutine receives an absolute path to the project as its only
+  parameter.
+
+  For example, if you use mod_perl to run the script, and have dumb
+  http protocol authentication configured for your repositories, you
+  can use the following hook to allow access only if the user is
+  authorized to read the files:
+
+    $export_auth_hook = sub {
+        use Apache2::SubRequest ();
+        use Apache2::Const -compile => qw(HTTP_OK);
+        my $path = "$_[0]/HEAD";
+        my $r    = Apache2::RequestUtil->request;
+        my $sub  = $r->lookup_file($path);
+        return $sub->filename eq $path
+            && $sub->status == Apache2::Const::HTTP_OK;
+    };
+
+
 Generating projects list using gitweb
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

gitweb/gitweb.perl

@@ -95,6 +95,11 @@ BEGIN
 # (only effective if this variable evaluates to true)
 our $export_ok = "++GITWEB_EXPORT_OK++";
 
+# show repository only if this subroutine returns true
+# when given the path to the project, for example:
+#    sub { return -e "$_[0]/git-daemon-export-ok"; }
+our $export_auth_hook = undef;
+
 # only allow viewing of repositories also shown on the overview page
 our $strict_export = "++GITWEB_STRICT_EXPORT++";
 
@@ -400,7 +405,8 @@ sub check_head_link {
 sub check_export_ok {
 	my ($dir) = @_;
 	return (check_head_link($dir) &&
-		(!$export_ok || -e "$dir/$export_ok"));
+		(!$export_ok || -e "$dir/$export_ok") &&
+		(!$export_auth_hook || $export_auth_hook->($dir)));
 }
 
 # process alternate names for backward compatibility