TACACS: T5577: Added `mandatory` and `optional` modes for TACACS+

In CLI we can choose authentication logic:

  - `mandatory` - if TACACS+ answered with `REJECT`, authentication must be
  stopped and access denied immediately.
  - `optional` (default) - if TACACS+ answers with `REJECT`, authentication
  continues using the next module.

In `mandatory` mode authentication will be stopped only if TACACS+ clearly
answered that access should be denied (no user in TACACS+ database, wrong
password, etc.). If TACACS+ is not available or other errors happen, it will be
skipped and authentication will continue with the next module, like in
`optional` mode.

7 files changed, 70 insertions, 23 deletions

diff --git a/debian/vyos-1x.postinst b/debian/vyos-1x.postinst
index a3c308e5f..860319edf 100644
--- a/debian/vyos-1x.postinst
+++ b/debian/vyos-1x.postinst
@@ -48,6 +48,11 @@ if grep -q '^tacacs' /etc/passwd; then
     fi
 fi
 
+# Remove TACACS+ PAM default profile
+if [[ -e /usr/share/pam-configs/tacplus ]]; then
+    rm /usr/share/pam-configs/tacplus
+fi
+
 # Add TACACS system users required for TACACS based system authentication
 if ! grep -q '^tacacs' /etc/passwd; then
     # Add the tacacs group and all 16 possible tacacs privilege-level users to
@@ -66,7 +71,6 @@ if ! grep -q '^tacacs' /etc/passwd; then
         adduser --quiet tacacs${level} adm
         adduser --quiet tacacs${level} dip
         adduser --quiet tacacs${level} users
-        adduser --quiet tacacs${level} aaa
         if [ $level -lt 15 ]; then
             adduser --quiet tacacs${level} vyattaop
             adduser --quiet tacacs${level} operator
diff --git a/debian/vyos-1x.preinst b/debian/vyos-1x.preinst
index 75fa5e7f1..861c5ec88 100644
--- a/debian/vyos-1x.preinst
+++ b/debian/vyos-1x.preinst
@@ -2,7 +2,6 @@ dpkg-divert --package vyos-1x --add --no-rename /etc/securetty
 dpkg-divert --package vyos-1x --add --no-rename /etc/security/capability.conf
 dpkg-divert --package vyos-1x --add --no-rename /lib/systemd/system/lcdproc.service
 dpkg-divert --package vyos-1x --add --no-rename /etc/logrotate.d/conntrackd
-dpkg-divert --package vyos-1x --add --no-rename /usr/share/pam-configs/tacplus
 dpkg-divert --package vyos-1x --add --no-rename /etc/rsyslog.conf
 dpkg-divert --package vyos-1x --add --no-rename /etc/skel/.bashrc
 dpkg-divert --package vyos-1x --add --no-rename /etc/skel/.profile
diff --git a/interface-definitions/system-login.xml.in b/interface-definitions/system-login.xml.in
index 71db8b1d6..30fea91b0 100644
--- a/interface-definitions/system-login.xml.in
+++ b/interface-definitions/system-login.xml.in
@@ -259,6 +259,26 @@
                   </constraint>
                 </properties>
               </leafNode>
+              <leafNode name="security-mode">
+                <properties>
+                  <help>Security mode for TACACS+ authentication</help>
+                  <completionHelp>
+                    <list>mandatory optional</list>
+                  </completionHelp>
+                  <valueHelp>
+                    <format>mandatory</format>
+                    <description>Deny access immediately if TACACS+ answers with REJECT</description>
+                  </valueHelp>
+                  <valueHelp>
+                    <format>optional</format>
+                    <description>Pass to the next authentication method if TACACS+ answers with REJECT</description>
+                  </valueHelp>
+                  <constraint>
+                    <regex>(mandatory|optional)</regex>
+                  </constraint>
+                </properties>
+                <defaultValue>optional</defaultValue>
+              </leafNode>
               #include <include/radius-timeout.xml.i>
               #include <include/interface/vrf.xml.i>
             </children>
diff --git a/src/conf_mode/system-login.py b/src/conf_mode/system-login.py
index be5ff2d4c..87a269499 100755
--- a/src/conf_mode/system-login.py
+++ b/src/conf_mode/system-login.py
@@ -389,11 +389,14 @@ def apply(login):
             pam_profile = 'radius-optional'
         cmd(f'pam-auth-update --enable {pam_profile}')
 
-    # Enable/Disable TACACS in PAM configuration
-    pam_cmd = '--remove'
+    # Enable/disable TACACS+ in PAM configuration
+    cmd('pam-auth-update --disable tacplus-mandatory tacplus-optional')
     if 'tacacs' in login:
-        pam_cmd = '--enable'
-    cmd(f'pam-auth-update --package {pam_cmd} tacplus')
+        if login['tacacs'].get('security_mode', '') == 'mandatory':
+            pam_profile = 'tacplus-mandatory'
+        else:
+            pam_profile = 'tacplus-optional'
+        cmd(f'pam-auth-update --enable {pam_profile}')
 
     return None
 
diff --git a/src/pam-configs/tacplus b/src/pam-configs/tacplus
deleted file mode 100644
index 66a1eaa4c..000000000
--- a/src/pam-configs/tacplus
+++ /dev/null
@@ -1,17 +0,0 @@
-Name: TACACS+ authentication
-Default: no
-Priority: 257
-Auth-Type: Primary
-Auth:
-    [default=ignore success=ignore] pam_succeed_if.so user ingroup aaa quiet
-    [authinfo_unavail=ignore success=end auth_err=bad default=ignore] pam_tacplus.so include=/etc/tacplus_servers login=login
-
-Account-Type: Primary
-Account:
-    [default=ignore success=ignore] pam_succeed_if.so user ingroup aaa quiet
-    [authinfo_unavail=ignore success=end perm_denied=bad default=ignore] pam_tacplus.so include=/etc/tacplus_servers login=login
-
-Session-Type: Additional
-Session:
-    [default=ignore success=ignore] pam_succeed_if.so user ingroup aaa quiet
-    [authinfo_unavail=ignore success=ok default=ignore] pam_tacplus.so include=/etc/tacplus_servers login=login
diff --git a/src/pam-configs/tacplus-mandatory b/src/pam-configs/tacplus-mandatory
new file mode 100644
index 000000000..92da02327
--- /dev/null
+++ b/src/pam-configs/tacplus-mandatory
@@ -0,0 +1,19 @@
+Name: TACACS+ authentication (mandatory mode)
+Default: no
+Priority: 576
+
+Auth-Type: Primary
+Auth-Initial:
+    [default=ignore success=end perm_denied=bad auth_err=bad] pam_tacplus.so include=/etc/tacplus_servers login=login
+Auth:
+    [default=ignore success=end perm_denied=bad auth_err=bad] pam_tacplus.so include=/etc/tacplus_servers login=login use_first_pass
+
+Account-Type: Primary
+Account:
+    [default=ignore success=1] pam_succeed_if.so user notingroup tacacs quiet
+    [default=ignore new_authtok_reqd=done success=end perm_denied=bad auth_err=bad] pam_tacplus.so include=/etc/tacplus_servers login=login
+
+Session-Type: Additional
+Session:
+    [default=ignore success=1] pam_succeed_if.so user notingroup tacacs quiet
+    [default=ignore success=ok perm_denied=bad auth_err=bad] pam_tacplus.so include=/etc/tacplus_servers login=login
diff --git a/src/pam-configs/tacplus-optional b/src/pam-configs/tacplus-optional
new file mode 100644
index 000000000..deed537d3
--- /dev/null
+++ b/src/pam-configs/tacplus-optional
@@ -0,0 +1,19 @@
+Name: TACACS+ authentication (optional mode)
+Default: no
+Priority: 576
+
+Auth-Type: Primary
+Auth-Initial:
+    [default=ignore success=end] pam_tacplus.so include=/etc/tacplus_servers login=login
+Auth:
+    [default=ignore success=end] pam_tacplus.so include=/etc/tacplus_servers login=login use_first_pass
+
+Account-Type: Primary
+Account:
+    [default=ignore success=1] pam_succeed_if.so user notingroup tacacs quiet
+    [default=ignore new_authtok_reqd=done success=end perm_denied=bad auth_err=bad] pam_tacplus.so include=/etc/tacplus_servers login=login
+
+Session-Type: Additional
+Session:
+    [default=ignore success=1] pam_succeed_if.so user notingroup tacacs quiet
+    [default=ignore success=ok perm_denied=bad auth_err=bad] pam_tacplus.so include=/etc/tacplus_servers login=login