--- loncom/interface/lonexttool.pm	2018/01/01 01:29:38	1.16
+++ loncom/interface/lonexttool.pm	2018/01/04 12:37:49	1.17
@@ -1,7 +1,7 @@
 # The LearningOnline Network with CAPA
 # Launch External Tool Provider (LTI)
 #
-# $Id: lonexttool.pm,v 1.16 2018/01/01 01:29:38 raeburn Exp $
+# $Id: lonexttool.pm,v 1.17 2018/01/04 12:37:49 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -274,8 +274,10 @@ sub lti_params {
     unless (grep(/^\Q$ltirole\E$/,@possroles)) {
         $ltirole = 'Learner';
     }
+    my @possdigest;
     my $digest_user = &Encode::decode_utf8($uname.':'.$udom);
     $digest_user = &Digest::SHA::sha1_hex($digest_user);
+    push(@possdigest,$digest_user);
     if ($env{'course.'.$env{'request.course.id'}.'.languages'} ne '') {
         @userlangs=(@userlangs,split(/\s*(\,|\;|\:)\s*/,
                     $env{'course.'.$env{'request.course.id'}.'.languages'}));
@@ -298,6 +300,7 @@ sub lti_params {
     if ($symb) {
         $digest_symb = &Encode::decode_utf8($symb);
         $digest_symb = &Digest::SHA::sha1_hex($digest_symb);
+        push(@possdigest,$digest_symb);
         my $navmap = Apache::lonnavmaps::navmap->new();
         if (ref($navmap)) {
             my $res = $navmap->getBySymb($symb);
@@ -338,6 +341,11 @@ sub lti_params {
             $crsprotocol = 'http';
         }
         if (($passback) || ($roster)) {
+            my (%currdigest,%digesthash);
+            if (@possdigest) {
+                %currdigest = &Apache::lonnet::get('exttools',\@possdigest,
+                                                   $cdom,$cnum);
+            }
             if ($passback) {
                 $ltiparams{'lis_outcome_service_url'} = $crsprotocol.'://'.$crshostname.'/adm/service/passback';
                 $ltiparams{'ext_ims_lis_basic_outcome_url'} = $ltiparams{'lis_outcome_service_url'};
@@ -355,18 +363,15 @@ sub lti_params {
                     }
                 }
             }
-            my %digesthash;
-            if ($ltiparams{'lis_result_sourcedid'}) {
-                $digesthash{$ltiparams{'lis_result_sourcedid'}} = "$idx\0".time; 
-            }
-            if ($ltiparams{'ext_ims_lis_memberships_id'}) {
-                $digesthash{$ltiparams{'ext_ims_lis_memberships_id'}} = "$idx\0".time; 
-            }
             if (($digest_symb) && ($gradesecret || $rostersecret)) {
-                $digesthash{$digest_symb} = $symb;
+                unless ((exists($currdigest{$digest_symb})) && ($currdigest{$digest_symb} eq $symb)) {
+                    $digesthash{$digest_symb} = $symb;
+                }
             }
             if (($passback) && ($gradesecret)) {
-                $digesthash{$digest_user} = $uname.':'.$udom;
+                unless ((exists($currdigest{$digest_user})) && ($currdigest{$digest_user} eq $uname.':'.$udom)) {
+                    $digesthash{$digest_user} = $uname.':'.$udom;
+                }
             }
             if (keys(%digesthash)) {
                 &Apache::lonnet::put('exttools',\%digesthash,$cdom,$cnum);