--- loncom/auth/lonacc.pm	2020/09/30 19:33:59	1.159.2.12
+++ loncom/auth/lonacc.pm	2020/10/23 21:33:46	1.159.2.15
@@ -1,7 +1,7 @@
 # The LearningOnline Network
 # Cookie Based Access Handler
 #
-# $Id: lonacc.pm,v 1.159.2.12 2020/09/30 19:33:59 raeburn Exp $
+# $Id: lonacc.pm,v 1.159.2.15 2020/10/23 21:33:46 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -563,31 +563,27 @@ sub handler {
         if ($env{'user.noloadbalance'} eq $r->dir_config('lonHostID')) {
             $checkexempt = 1;
         }
-        unless ($checkexempt) {
+        unless (($checkexempt) || (($requrl eq '/adm/switchserver') && (!$r->is_initial_req()))) {
             ($is_balancer,$otherserver) =
                 &Apache::lonnet::check_loadbalancing($env{'user.name'},
                                                      $env{'user.domain'});
             if ($is_balancer) {
-                unless (($requrl eq '/adm/switchserver') && (!$r->is_initial_req())) {
-                    # Check if browser sent a LON-CAPA load balancer cookie (and this is a balancer)
-                    my ($found_server,$balancer_cookie) = &Apache::lonnet::check_for_balancer_cookie($r);
-                    if (($found_server) && ($balancer_cookie =~ /^\Q$env{'user.domain'}\E_\Q$env{'user.name'}\E_/)) {
-                        $otherserver = $found_server;
-                    }
+                # Check if browser sent a LON-CAPA load balancer cookie (and this is a balancer)
+                my ($found_server,$balancer_cookie) = &Apache::lonnet::check_for_balancer_cookie($r);
+                if (($found_server) && ($balancer_cookie =~ /^\Q$env{'user.domain'}\E_\Q$env{'user.name'}\E_/)) {
+                    $otherserver = $found_server;
+                }
+                unless ($requrl eq '/adm/switchserver') {
+                    $r->set_handlers('PerlResponseHandler'=>
+                                     [\&Apache::switchserver::handler]);
                 }
-            }
-        }
-        if ($is_balancer) {
-            unless (($requrl eq '/adm/switchserver') && (!$r->is_initial_req())) {
-                $r->set_handlers('PerlResponseHandler'=>
-                                 [\&Apache::switchserver::handler]);
                 if ($otherserver ne '') {
                     $env{'form.otherserver'} = $otherserver;
                 }
-            }
-            unless (($env{'form.origurl'}) || ($r->uri eq '/adm/roles') ||
-                    ($r->uri eq '/adm/switchserver') || ($r->uri eq '/adm/sso')) {
-                $env{'form.origurl'} = $r->uri;
+                unless (($env{'form.origurl'}) || ($r->uri eq '/adm/roles') ||
+                        ($r->uri eq '/adm/switchserver') || ($r->uri eq '/adm/sso')) {
+                    $env{'form.origurl'} = $r->uri;
+                }
             }
         }
 
@@ -617,6 +613,9 @@ sub handler {
                     my $query = $r->args;
                     foreach my $pair (split(/&/,$query)) {
                         my ($name, $value) = split(/=/,$pair);
+                        $name = &unescape($name);
+                        $value =~ tr/+/ /;
+                        $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",hex($1))/eg;
                         if ($name eq 'symb') {
                             $poss_symb = &Apache::lonnet::symbclean($value);
                             last;
@@ -777,19 +776,29 @@ sub handler {
                         unless (&Apache::lonnet::symbverify($symb,$requrl,\$encstate)) {
                             $invalidsymb = 1;
                             #
-                            # If $env{'request.enc'} is true, but no encryption for $symb retrieved
-                            # by original lonnet::symbread() call, call again to check for an instance
-                            # of $requrl in the course which has encryption, and set that as the symb.
-                            # If there is no such symb, or symbverify() fails for the new symb proceed
-                            # to report invalid symb.
+                            # If $env{'request.enc'} inconsistent with encryption expected for $symb
+                            # retrieved by lonnet::symbread(), call again to check for an instance of
+                            # $requrl in the course for which expected encryption matches request.enc.
+                            # If symb for different instance passes lonnet::symbverify(), use that as
+                            # the symb for $requrl and call &Apache::lonnet::allowed() for that symb.
+                            # Report invalid symb if there is no other symb. Redirect to /adm/ambiguous
+                            # if multiple possible symbs consistent with request.enc available for $requrl.
                             #
-                            if ($env{'request.enc'} && !$encstate) {
+                            if (($env{'request.enc'} && !$encstate) || (!$env{'request.enc'} && $encstate)) {
                                 my %possibles;
                                 my $nocache = 1;
+                                my $oldsymb = $symb;
                                 $symb = &Apache::lonnet::symbread($requrl,'','','',\%possibles,$nocache);
-                                if ($symb) {
+                                if (($symb) && ($symb ne $oldsymb)) {
                                     if (&Apache::lonnet::symbverify($symb,$requrl)) {
-                                        $invalidsymb = '';
+                                        my $access=&Apache::lonnet::allowed('bre',$requrl,$symb);
+                                        if ($access eq 'B') {
+                                            $env{'request.symb'} = $symb;
+                                            &Apache::blockedaccess::setup_handler($r);
+                                            return OK;
+                                        } elsif (($access eq '2') || ($access eq 'F')) {
+                                            $invalidsymb = '';
+                                        }
                                     }
                                 } elsif (keys(%possibles) > 1) {
                                     $r->internal_redirect('/adm/ambiguous');