--- loncom/auth/lonauth.pm	2011/02/24 23:37:50	1.111
+++ loncom/auth/lonauth.pm	2021/01/04 03:48:29	1.121.2.21
@@ -1,7 +1,7 @@
 # The LearningOnline Network
 # User Authentication Module
 #
-# $Id: lonauth.pm,v 1.111 2011/02/24 23:37:50 raeburn Exp $
+# $Id: lonauth.pm,v 1.121.2.21 2021/01/04 03:48:29 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -32,21 +32,20 @@ use strict;
 use LONCAPA;
 use Apache::Constants qw(:common);
 use CGI qw(:standard);
-use DynaLoader; # for Crypt::DES version
-use Crypt::DES;
 use Apache::loncommon();
 use Apache::lonnet;
 use Apache::lonmenu();
 use Apache::createaccount;
 use Fcntl qw(:flock);
 use Apache::lonlocal;
-use Apache::File ();
+use Apache::File();
 use HTML::Entities;
+use Digest::MD5;
  
 # ------------------------------------------------------------ Successful login
 sub success {
     my ($r, $username, $domain, $authhost, $lowerurl, $extra_env,
-	$form) = @_;
+	$form,$cid) = @_;
 
 # ------------------------------------------------------------ Get cookie ready
     my $cookie =
@@ -60,8 +59,9 @@ sub success {
 
 # -------------------------------------------------------------------- Log this
 
+    my $ip = &Apache::lonnet::get_requestor_ip();
     &Apache::lonnet::log($domain,$username,$authhost,
-                         "Login $ENV{'REMOTE_ADDR'}");
+                         "Login $ip");
 
 # ------------------------------------------------- Check for critical messages
 
@@ -72,8 +72,27 @@ sub success {
         }
     }
 
-# ------------------------------------------------------------ Get cookie ready
-    $cookie="lonID=$cookie; path=/";
+# ------------------------------------------------------------ Get cookies ready
+    my ($securecookie,$defaultcookie);
+    my $ssl = $r->subprocess_env('https');
+    if ($ssl) {
+        $securecookie="lonSID=$cookie; path=/; HttpOnly; secure";
+        my $lonidsdir=$r->dir_config('lonIDsDir');
+        if (($lonidsdir) && (-e "$lonidsdir/$cookie.id")) {
+            my $linkname=substr(Digest::MD5::md5_hex(Digest::MD5::md5_hex(time(). {}. rand(). $$)), 0, 32).'_linked';
+            if (-e "$lonidsdir/$linkname.id") {
+                unlink("$lonidsdir/$linkname.id");
+            }
+            my $made_symlink = eval { symlink("$lonidsdir/$cookie.id",
+                                              "$lonidsdir/$linkname.id"); 1 };
+            if ($made_symlink) {
+                $defaultcookie = "lonLinkID=$linkname; path=/; HttpOnly;";
+                &Apache::lonnet::appenv({'user.linkedenv' => $linkname});
+            }
+        }
+    } else {
+        $defaultcookie = "lonID=$cookie; path=/; HttpOnly;";
+    }
 # -------------------------------------------------------- Menu script and info
     my $destination = $lowerurl;
 
@@ -99,20 +118,28 @@ sub success {
     }
     if (defined($form->{symb})) {
         my $destsymb = $form->{symb};
+        my $encrypted;
+        if ($destsymb =~ m{^/enc/}) {
+            $encrypted = 1;
+            if ($cid) {
+                $destsymb = &Apache::lonenc::unencrypted($destsymb,$cid);
+            }
+        }
         $destination  .= ($destination =~ /\?/) ? '&' : '?';
         if ($destsymb =~ /___/) {
-            # FIXME Need to deal with encrypted symbs and urls as needed.
             my ($map,$resid,$desturl)=split(/___/,$destsymb);
-            unless ($desturl=~/^(adm|uploaded|editupload|public)/) {
-                $desturl = &Apache::lonnet::clutter($desturl);
+            $desturl = &Apache::lonnet::clutter($desturl);
+            if ($encrypted) {
+                $desturl = &Apache::lonenc::encrypted($desturl,1,$cid);
+                $destsymb = $form->{symb};
             }
             $desturl = &HTML::Entities::encode($desturl,'"<>&');
             $destsymb = &HTML::Entities::encode($destsymb,'"<>&');
-            $destination .= '&destinationurl='.$desturl.
+            $destination .= 'destinationurl='.$desturl.
                             '&destsymb='.$destsymb;
-        } else {
+        } elsif (!$encrypted) {
             $destsymb = &HTML::Entities::encode($destsymb,'"<>&');
-            $destination .= '&destinationurl='.$destsymb;
+            $destination .= 'destinationurl='.$destsymb;
         }
     }
     if ($destination =~ m{^/adm/roles}) {
@@ -120,62 +147,111 @@ sub success {
         $destination .= 'source=login';
     }
 
-    my $windowinfo = Apache::lonhtmlcommon::scripttag('self.name="loncapaclient";');
-    my $header = '<meta HTTP-EQUIV="Refresh" CONTENT="0; url='.$destination.'" />';
+    my $windowinfo=&Apache::lonmenu::open($env{'browser.os'});
+    my $startupremote=&Apache::lonmenu::startupremote($destination);
+    my $remoteinfo=&Apache::lonmenu::load_remote_msg($lowerurl);
+    my $setflags=&Apache::lonmenu::setflags();
+    my $maincall=&Apache::lonmenu::maincall();
     my $brcrum = [{'href' => '',
                    'text' => 'Successful Login'},];
     my $start_page=&Apache::loncommon::start_page('Successful Login',
-                                                  $header,
-                                                  {'bread_crumbs' => $brcrum,});
+                                                  $startupremote,
+                                                  {'no_inline_link' => 1,
+                                                   'bread_crumbs' => $brcrum,});
     my $end_page  =&Apache::loncommon::end_page();
 
-	my $continuelink='<a href="'.$destination.'">'.&mt('Continue').'</a>';
+    my $continuelink;
+    if ($env{'environment.remote'} eq 'off') {
+	$continuelink='<a href="'.$destination.'">'.&mt('Continue').'</a>';
+    }
 # ------------------------------------------------- Output for successful login
 
     &Apache::loncommon::content_type($r,'text/html');
-    $r->header_out('Set-cookie' => $cookie);
+    if ($securecookie) {
+        $r->headers_out->add('Set-cookie' => $securecookie);
+    }
+    if ($defaultcookie) {
+        $r->headers_out->add('Set-cookie' => $defaultcookie);
+    }
     $r->send_http_header;
 
     my %lt=&Apache::lonlocal::texthash(
 				       'wel' => 'Welcome',
-				       'mes' => 'Welcome to the Learning<i>Online</i> Network with CAPA. Please wait while your session is being set up.',
 				       'pro' => 'Login problems?',
-				       'log' => 'loginproblems.html',
 				       );
+    my $loginhelp = &loginhelpdisplay($domain);
+    if ($loginhelp) {
+        $loginhelp = '<p><a href="'.$loginhelp.'">'.$lt{'pro'}.'</a></p>';
+    }
+
+    my $welcome = &mt('Welcome to the Learning[_1]Online[_2] Network with CAPA. Please wait while your session is being set up.','<i>','</i>'); 
     $r->print(<<ENDSUCCESS);
 $start_page
+$setflags
 $windowinfo
 <h1>$lt{'wel'}</h1>
-$lt{'mes'}<p>
-<a href="/adm/$lt{'log'}">$lt{'pro'}</a></p>
+$welcome
+$loginhelp
+$remoteinfo
+$maincall
 $continuelink
 $end_page
 ENDSUCCESS
+    return;
 }
 
 # --------------------------------------------------------------- Failed login!
 
 sub failed {
     my ($r,$message,$form) = @_;
-    my $start_page = &Apache::loncommon::start_page('Unsuccessful Login',undef);
-    my $retry = '/adm/login?username='.$form->{'uname'}.
-                '&domain='.$form->{'udom'};
+    (undef,undef,undef,my $clientmathml,my $clientunicode) =
+        &Apache::loncommon::decode_user_agent();
+    my $args = {};
+    if ($clientunicode && !$clientmathml) {
+        $args = {'browser.unicode' => 1};
+    }
+
+    my $start_page = &Apache::loncommon::start_page('Unsuccessful Login',undef,$args);
+    my $uname = &Apache::loncommon::cleanup_html($form->{'uname'});
+    my $udom = &Apache::loncommon::cleanup_html($form->{'udom'});
+    if (&Apache::lonnet::domain($udom,'description') eq '') {
+        undef($udom);
+    }
+    my $retry = '/adm/login';
+    if ($uname eq $form->{'uname'}) {
+        $retry .= '?username='.$uname;
+    }
+    if ($udom) {
+        $retry .= (($retry=~/\?/)?'&amp;':'?').'domain='.$udom;
+    }
     if (exists($form->{role})) {
-        $retry .= '&role='.$form->{role};
+        my $role = &Apache::loncommon::cleanup_html($form->{role});
+        if ($role ne '') {
+            $retry .= (($retry=~/\?/)?'&amp;':'?').'role='.$role;
+        }
     }
     if (exists($form->{symb})) {
-        $retry .= '&symb='.$form->{symb};
+        my $symb = &Apache::loncommon::cleanup_html($form->{symb});
+        if ($symb ne '') {
+            $retry .= (($retry=~/\?/)?'&amp;':'?').'symb='.$symb;
+        }
     }
-    my $end_page   = &Apache::loncommon::end_page();
+    my $end_page = &Apache::loncommon::end_page();
     &Apache::loncommon::content_type($r,'text/html');
     $r->send_http_header;
+    my @actions =
+         (&mt('Please [_1]log in again[_2].','<a href="'.$retry.'">','</a>'));
+    my $loginhelp = &loginhelpdisplay($udom);
+    if ($loginhelp) {
+        push(@actions, '<a href="'.$loginhelp.'">'.&mt('Login problems?').'</a>');
+    }
+    #FIXME: link to helpdesk might be added here
+
     $r->print(
        $start_page
-      .'<h1>'.&mt('Sorry ...').'</h1>'
-      .'<p class="LC_warning">'.&mt($message).'</p>'
-      .'<p>'.&mt('Please [_1]log in again[_2].','<a href="'.$retry.'">','</a>')
-      .'</p>'
-      .'<p><a href="/adm/loginproblems.html">'.&mt('Login problems?').'</a></p>'
+      .'<h2>'.&mt('Sorry ...').'</h2>'
+      .&Apache::lonhtmlcommon::confirm_success(&mt($message),1).'<br /><br />'
+      .&Apache::lonhtmlcommon::actionbox(\@actions)
       .$end_page
     );
  }
@@ -186,18 +262,18 @@ sub reroute {
     my ($r) = @_;
     &Apache::loncommon::content_type($r,'text/html');
     $r->send_http_header;
-    my $msg='<h1>'.&mt('Sorry ...').'</h1>'
+    my $msg='<b>'.&mt('Sorry ...').'</b><br />'
            .&mt('Please [_1]log in again[_2].');
-    &Apache::loncommon::simple_error_page($r,'Rerouting',$msg);
+    &Apache::loncommon::simple_error_page($r,'Rerouting',$msg,{'no_auto_mt_msg' => 1});
 }
 
 # ---------------------------------------------------------------- Main handler
 
 sub handler {
     my $r = shift;
-    my $form;
+    my $londocroot = $r->dir_config('lonDocRoot');
 # Are we re-routing?
-    if (-e '/home/httpd/html/lon-status/reroute.txt') {
+    if (-e "$londocroot/lon-status/reroute.txt") {
 	&reroute($r);
 	return OK;
     }
@@ -226,7 +302,7 @@ sub handler {
             }
             $r->print(
                $start_page
-              .'<h1>'.&mt('You are already logged in!').'</h1>'
+              .'<p class="LC_warning">'.&mt('You are already logged in!').'</p>'
               .'<p>'.&mt('Please either [_1]continue the current session[_2] or [_3]log out[_4].'
                     ,'<a href="'.$dest.'">','</a>','<a href="/adm/logout">','</a>')
               .'</p>'
@@ -249,7 +325,7 @@ sub handler {
        $value =~ tr/+/ /;
        $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",hex($1))/eg;
        $form{$name}=$value;
-    } 
+    }
 
     if ((!$form{'uname'}) || (!$form{'upass0'}) || (!$form{'udom'})) {
 	&failed($r,'Username, password and domain need to be specified.',
@@ -259,10 +335,11 @@ sub handler {
 
 # split user logging in and "su"-user
 
-    ($form{'uname'},$form{'suname'})=split(/\:/,$form{'uname'});
+    ($form{'uname'},$form{'suname'},$form{'sudom'})=split(/\:/,$form{'uname'});
     $form{'uname'} = &LONCAPA::clean_username($form{'uname'});
     $form{'suname'}= &LONCAPA::clean_username($form{'suname'});
-    $form{'udom'}  = &LONCAPA::clean_domain(  $form{'udom'});
+    $form{'udom'}  = &LONCAPA::clean_domain($form{'udom'});
+    $form{'sudom'} = &LONCAPA::clean_domain($form{'sudom'});
 
     my $role   = $r->dir_config('lonRole');
     my $domain = $r->dir_config('lonDefDomain');
@@ -274,7 +351,8 @@ sub handler {
     my $tmpinfo=Apache::lonnet::reply('tmpget:'.$form{'logtoken'},
                                       $form{'serverid'});
 
-    if (($tmpinfo=~/^error/) || ($tmpinfo eq 'con_lost')) {
+    if (($tmpinfo=~/^error/) || ($tmpinfo eq 'con_lost') || 
+        ($tmpinfo eq 'no_such_host')) {
 	&failed($r,'Information needed to verify your login information is missing, inaccessible or expired.',\%form);
         return OK;
     } else {
@@ -292,57 +370,38 @@ sub handler {
         return OK;
     }
 
-    my ($key,$firsturl,$rolestr,$symbstr)=split(/&/,$tmpinfo);
+    my ($key,$firsturl,$rolestr,$symbstr,$iptokenstr)=split(/&/,$tmpinfo);
     if ($rolestr) {
         $rolestr = &unescape($rolestr);
     }
     if ($symbstr) {
         $symbstr= &unescape($symbstr);
     }
+    if ($iptokenstr) {
+        $iptokenstr = &unescape($iptokenstr);
+    }
     if ($rolestr =~ /^role=/) {
         (undef,$form{'role'}) = split('=',$rolestr);
     }
     if ($symbstr =~ /^symb=/) { 
         (undef,$form{'symb'}) = split('=',$symbstr);
     }
-
-    my $keybin=pack("H16",$key);
-
-    my $cipher;
-    if ($Crypt::DES::VERSION>=2.03) {
-	$cipher=new Crypt::DES $keybin;
-    }
-    else {
-	$cipher=new DES $keybin;
+    if ($iptokenstr =~ /^iptoken=/) {
+        (undef,$form{'iptoken'}) = split('=',$iptokenstr);
     }
-    my $upass='';
-    for (my $i=0;$i<=2;$i++) {
-	my $chunk=
-	    $cipher->decrypt(unpack("a8",pack("H16",substr($form{'upass'.$i},0,16))));
 
-	$chunk.=
-	    $cipher->decrypt(unpack("a8",pack("H16",substr($form{'upass'.$i},16,16))));
-
-	$chunk=substr($chunk,1,ord(substr($chunk,0,1)));
-	$upass.=$chunk;
-    }
+    my $upass = &Apache::loncommon::des_decrypt($key,$form{'upass0'});
 
 # ---------------------------------------------------------------- Authenticate
-    my @cancreate;
+
     my %domconfig = &Apache::lonnet::get_dom('configuration',['usercreation'],$form{'udom'});
-    if (ref($domconfig{'usercreation'}) eq 'HASH') {
-        if (ref($domconfig{'usercreation'}{'cancreate'}) eq 'HASH') {
-            if (ref($domconfig{'usercreation'}{'cancreate'}{'selfcreate'}) eq 'ARRAY') {
-                @cancreate = @{$domconfig{'usercreation'}{'cancreate'}{'selfcreate'}};
-            } elsif (($domconfig{'usercreation'}{'cancreate'}{'selfcreate'} ne 'none') && 
-                     ($domconfig{'usercreation'}{'cancreate'}{'selfcreate'} ne '')) {
-                @cancreate = ($domconfig{'usercreation'}{'cancreate'}{'selfcreate'});
-            }
-        }
-    }
+    my ($cancreate,$statustocreate) =
+        &Apache::createaccount::get_creation_controls($form{'udom'},$domconfig{'usercreation'});
     my $defaultauth;
-    if (grep(/^login$/,@cancreate)) {
-        $defaultauth = 1;
+    if (ref($cancreate) eq 'ARRAY') {
+        if (grep(/^login$/,@{$cancreate})) {
+            $defaultauth = 1;
+        }
     }
     my $clientcancheckhost = 1;
     my $authhost=Apache::lonnet::authenticate($form{'uname'},$upass,
@@ -356,24 +415,25 @@ sub handler {
 		\%form);
         return OK;
     } elsif ($authhost eq 'no_account_on_host') {
-        my %domconfig = 
-            &Apache::lonnet::get_dom('configuration',['usercreation'],$form{'udom'});
-        if (grep(/^login$/,@cancreate)) {
+        if ($defaultauth) {
             my $domdesc = &Apache::lonnet::domain($form{'udom'},'description');
             unless (&check_can_host($r,\%form,'no_account_on_host',$domdesc)) {
                 return OK;
             }
             my $start_page = 
-                &Apache::loncommon::start_page('Create a user account in LON-CAPA');
+                &Apache::loncommon::start_page('Create a user account in LON-CAPA',
+                                               '',{'no_inline_link'   => 1,});
             my $lonhost = $r->dir_config('lonHostID');
             my $origmail = $Apache::lonnet::perlvar{'lonSupportEMail'};
             my $contacts = 
                 &Apache::loncommon::build_recipient_list(undef,'helpdeskmail',
                                                         $form{'udom'},$origmail);
             my ($contact_email) = split(',',$contacts); 
-            my $output = &Apache::createaccount::username_check($form{'uname'}, 
-                                                                $form{'udom'},$domdesc,'',
-                                                                $lonhost,$contact_email,$contact_name);
+            my $output = 
+                &Apache::createaccount::username_check($form{'uname'},$form{'udom'},
+                                                       $domdesc,'',$lonhost,
+                                                       $contact_email,$contact_name,
+                                                       undef,$statustocreate);
             &Apache::loncommon::content_type($r,'text/html');
             $r->send_http_header;
             &Apache::createaccount::print_header($r,$start_page);
@@ -391,22 +451,81 @@ sub handler {
 	($firsturl=~/^\/adm\/(logout|remote)/)) {
 	$firsturl='/adm/roles';
     }
+
+    my $hosthere;
+    if ($form{'iptoken'}) {
+        my %sessiondata = &Apache::lonnet::tmpget($form{'iptoken'});
+        my $delete = &Apache::lonnet::tmpdel($form{'iptoken'});
+        if (($sessiondata{'domain'} eq $form{'udom'}) &&
+            ($sessiondata{'username'} eq $form{'uname'})) {
+            $hosthere = 1;
+        }
+    }
+
 # --------------------------------- Are we attempting to login as somebody else?
     if ($form{'suname'}) {
+        my ($suname,$sudom,$sudomref);
+        $suname = $form{'suname'};
+        $sudom = $form{'udom'};
+        if ($form{'sudom'}) {
+            unless ($sudom eq $form{'sudom'}) {
+                if (&Apache::lonnet::domain($form{'sudom'})) {
+                    $sudomref = [$form{'sudom'}];
+                    $sudom = $form{'sudom'};
+                }
+            }
+        }
 # ------------ see if the original user has enough privileges to pull this stunt
-	if (&Apache::lonnet::privileged($form{'uname'},$form{'udom'})) {
+	if (&Apache::lonnet::privileged($form{'uname'},$form{'udom'},$sudomref)) {
 # ---------------------------------------------------- see if the su-user exists
-	    unless (&Apache::lonnet::homeserver($form{'suname'},$form{'udom'})
-		eq 'no_host') {
-		&Apache::lonnet::logthis(&Apache::lonnet::homeserver($form{'suname'},$form{'udom'}));
+	    unless (&Apache::lonnet::homeserver($suname,$sudom) eq 'no_host') {
 # ------------------------------ see if the su-user is not too highly privileged
-		unless (&Apache::lonnet::privileged($form{'suname'},$form{'udom'})) {
+		if (&Apache::lonnet::privileged($suname,$sudom)) {
+                    &Apache::lonnet::logthis('Attempted switch user to privileged user');
+                } else {
+                    my $noprivswitch;
+#
+# su-user's home server and user's home server must have one of:
+# (a) same domain
+# (b) same primary library server for the two domains
+# (c) same "internet domain" for primary library server(s) for home servers' domains
+#
+                    my $suprim = &Apache::lonnet::domain($sudom,'primary');
+                    my $suintdom = &Apache::lonnet::internet_dom($suprim);
+                    unless ($sudom eq $form{'udom'}) {
+                        my $uprim = &Apache::lonnet::domain($form{'udom'},'primary');
+                        my $uintdom = &Apache::lonnet::internet_dom($uprim);
+                        unless ($suprim eq $uprim) {
+                            unless ($suintdom eq $uintdom) {
+                                &Apache::lonnet::logthis('Attempted switch user '
+                                   .'to user with different "internet domain".');
+                                $noprivswitch = 1;
+                            }
+                        }
+                    }
+
+                    unless ($noprivswitch) {
+#
+# server where log-in occurs must have same "internet domain" as su-user's home
+# server
+#
+                        my $lonhost = $r->dir_config('lonHostID');
+                        my $hostintdom = &Apache::lonnet::internet_dom($lonhost);
+                        if ($hostintdom ne $suintdom) {
+                            &Apache::lonnet::logthis('Attempted switch user on a '
+                                .'server with a different "internet domain".');
+                        } else {
+
 # -------------------------------------------------------- actually switch users
-		    &Apache::lonnet::logperm('User '.$form{'uname'}.' at '.$form{'udom'}.
-			' logging in as '.$form{'suname'});
-		    $form{'uname'}=$form{'suname'};
-		} else {
-		    &Apache::lonnet::logthis('Attempted switch user to privileged user');
+
+			    &Apache::lonnet::logperm('User '.$form{'uname'}.' at '.
+				$form{'udom'}.' logging in as '.$suname.':'.$sudom);
+			    $form{'uname'}=$suname;
+                            if ($form{'udom'} ne $sudom) {
+                                $form{'udom'}=$sudom;
+                            }
+                        }
+                    }
 		}
 	    }
 	} else {
@@ -414,17 +533,79 @@ sub handler {
 	}
     }
 
-    unless (&check_can_host($r,\%form,$authhost)) {
-        return OK;
+    my ($is_balancer,$otherserver);
+
+    unless ($hosthere) {
+        ($is_balancer,$otherserver) =
+            &Apache::lonnet::check_loadbalancing($form{'uname'},$form{'udom'},'login');
+        if ($is_balancer) {
+            # 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 = $found_server;
+            }
+            if ($otherserver eq '') {
+                my $lowest_load;
+                ($otherserver,undef,undef,undef,$lowest_load) = &Apache::lonnet::choose_server($form{'udom'});
+                if ($lowest_load > 100) {
+                    $otherserver = &Apache::lonnet::spareserver($lowest_load,$lowest_load,1,$form{'udom'});
+                }
+            }
+            if ($otherserver ne '') {
+                my @hosts = &Apache::lonnet::current_machine_ids();
+                if (grep(/^\Q$otherserver\E$/,@hosts)) {
+                    $hosthere = $otherserver;
+                }
+            }
+        }
     }
 
-    if ($r->dir_config("lonBalancer") eq 'yes') {
-	&success($r,$form{'uname'},$form{'udom'},$authhost,'noredirect',undef,
-		 \%form);
-        my ($otherserver) = &Apache::lonnet::choose_server($form{'udom'});
-	$r->internal_redirect('/adm/switchserver?otherserver='.$otherserver.'&origurl='.$firsturl);
+    if (($is_balancer) && (!$hosthere)) {
+        if ($otherserver) {
+            &success($r,$form{'uname'},$form{'udom'},$authhost,'noredirect',undef,
+                     \%form);
+            my $switchto = '/adm/switchserver?otherserver='.$otherserver;
+            if (($firsturl) && ($firsturl ne '/adm/switchserver') && ($firsturl ne '/adm/roles')) {
+                $switchto .= '&origurl='.$firsturl;
+            }
+            if ($form{'role'}) {
+                $switchto .= '&role='.$form{'role'};
+            }
+            if ($form{'symb'}) {
+                $switchto .= '&symb='.$form{'symb'};
+            }
+            $r->internal_redirect($switchto);
+        } else {
+            &Apache::loncommon::content_type($r,'text/html');
+            $r->send_http_header;
+            $r->print(&noswitch());
+        }
         return OK;
     } else {
+        if (!&check_can_host($r,\%form,$authhost)) {
+            my ($otherserver) = &Apache::lonnet::choose_server($form{'udom'});
+            if ($otherserver) {
+                &success($r,$form{'uname'},$form{'udom'},$authhost,'noredirect',undef,
+                         \%form);
+                my $switchto = '/adm/switchserver?otherserver='.$otherserver;
+                if (($firsturl) && ($firsturl ne '/adm/switchserver') && ($firsturl ne '/adm/roles')) {
+                    $switchto .= '&origurl='.$firsturl;
+                }
+                if ($form{'role'}) {
+                    $switchto .= '&role='.$form{'role'};
+                }
+                if ($form{'symb'}) {
+                    $switchto .= '&symb='.$form{'symb'};
+                }
+                $r->internal_redirect($switchto);
+            } else {
+                &Apache::loncommon::content_type($r,'text/html');
+                $r->send_http_header;
+                $r->print(&noswitch());
+            }
+            return OK;
+        }
+
 # ------------------------------------------------------- Do the load balancing
 
 # ---------------------------------------------------------- Determine own load
@@ -441,6 +622,9 @@ sub handler {
 # ---------------------------------------------------------- Are we overloaded?
         if ((($userloadpercent>100.0)||($loadpercent>100.0))) {
             my $unloaded=Apache::lonnet::spareserver($loadpercent,$userloadpercent,1,$form{'udom'});
+            if (!$unloaded) {
+                ($unloaded) = &Apache::lonnet::choose_server($form{'udom'});
+            }
             if ($unloaded) {
                 &success($r,$form{'uname'},$form{'udom'},$authhost,'noredirect',
                          undef,\%form);
@@ -448,6 +632,9 @@ sub handler {
                 return OK;
             }
         }
+        if (($is_balancer) && ($hosthere)) {
+            $form{'noloadbalance'} = $hosthere;
+        }
         &success($r,$form{'uname'},$form{'udom'},$authhost,$firsturl,undef,
                  \%form);
         return OK;
@@ -486,7 +673,9 @@ sub check_can_host {
     }
     unless ($canhost) {
         if ($authhost eq 'no_account_on_host') {
-            my ($login_host,$hostname) = &Apache::lonnet::choose_server($udom);
+            my $checkloginvia = 1;
+            my ($login_host,$hostname) = 
+                &Apache::lonnet::choose_server($udom,$checkloginvia);
             &Apache::loncommon::content_type($r,'text/html');
             $r->send_http_header;
             if ($login_host ne '') {
@@ -516,6 +705,42 @@ sub check_can_host {
     return $canhost;
 }
 
+sub noswitch {
+    my $result = &Apache::loncommon::start_page('Access to LON-CAPA unavailable').
+                 '<h3>'.&mt('Session unavailable').'</h3>'.
+                 &mt('This LON-CAPA server is unable to host your session.').'<br />'.
+                 '<p>'.&mt('Currently no other LON-CAPA server is available to host your session either.').'</p>'.
+                 &Apache::loncommon::end_page();
+    return $result;
+}
+
+sub loginhelpdisplay {
+    my ($authdomain) = @_;
+    my $login_help = 1;
+    my $lang = &Apache::lonlocal::current_language();
+    if ($login_help) {
+        my $dom = $authdomain;
+        if ($dom eq '') {
+            $dom = &Apache::lonnet::default_login_domain();
+        }
+        my %domconfhash = &Apache::loncommon::get_domainconf($dom);
+        my $loginhelp_url;
+        if ($lang) {
+            $loginhelp_url = $domconfhash{$dom.'.login.helpurl_'.$lang};
+            if ($loginhelp_url ne '') {
+                return $loginhelp_url;
+            }
+        }
+        $loginhelp_url = $domconfhash{$dom.'.login.helpurl_nolang'};
+        if ($loginhelp_url ne '') {
+            return $loginhelp_url;
+        } else {
+            return '/adm/loginproblems.html';
+        }
+    }
+    return;
+}
+
 1;
 __END__