Internet-Draft YANG for TACACS+ over TLS May 2024
Boucadair Expires 29 November 2024 [Page]
Workgroup:
Operations and Management Area Working Group
Internet-Draft:
draft-boucadair-opsawg-secure-tacacs-yang-01
Published:
Intended Status:
Informational
Expires:
Author:
M. Boucadair, Ed.
Orange

A YANG Model for Terminal Access Controller Access-Control System Plus (TACACS+) over TLS 1.3

Abstract

This document defines a YANG module for Terminal Access Controller Access-Control System Plus (TACACS+) over TLS 1.3. This modules augments the YANG Data Model for Terminal Access Controller Access-Control System Plus (TACACS+) defined in the RFC 9105 with TLS-related data nodes.

About This Document

This note is to be removed before publishing as an RFC.

The latest revision of this draft can be found at https://boucadair.github.io/secure-tacacs-yang/draft-boucadair-opsawg-secure-tacacs-yang.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-boucadair-opsawg-secure-tacacs-yang/.

Discussion of this document takes place on the Operations and Management Area Working Group Working Group mailing list (mailto:opsawg@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/opsawg/. Subscribe at https://www.ietf.org/mailman/listinfo/opsawg/.

Source for this draft and an issue tracker can be found at https://github.com/boucadair/secure-tacacs-yang.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 29 November 2024.

▲

Table of Contents

1. Introduction

[RFC9105] defines a YANG module ("ietf-system-tacacs-plus") that augments the System Management data model defined in [RFC7317] for the management of Terminal Access Controller Access-Control System Plus (TACACS+) clients. Typically, the "ietf-system-tacacs-plus" module is used to configure a TACACS+ client on a device to support deployment scenarios with centralized authentication, authorization, and accounting servers.

This document defines a YANG module for managing TACACS+ over TLS 1.3 clients [I-D.ietf-opsawg-tacacs-tls13]. The module is designed as an augmentation to the "ietf-system-tacacs-plus" module specified in [RFC9105].

The module leverages the TLS structures defined in [I-D.ietf-netconf-tls-client-server]. Concretely, this first version of the specification uses a pruning approach rather that a reuse of the groupings defined in [I-D.ietf-netconf-tls-client-server].

2. Conventions and Definitions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

The meanings of the symbols in the YANG tree diagrams are defined in [RFC8340].

The document uses the terms defined in Section 2 of [I-D.ietf-opsawg-tacacs-tls13] and Section 3 of [RFC8907].

'client' refers to TLS TACACS+ client, while 'server' refers to TLS TACACS+ server.

3. Module Tree Structure

The module is designed to cover the following key requirements specified in [I-D.ietf-opsawg-tacacs-tls13]:

The full tree structure is shown below:

=============== NOTE: '\' line wrapping per RFC 8792 ================

module: ietf-system-secure-tacacs

  augment /sys:system/sys-tcs-plus:tacacs-plus/sys-tcs-plus:server:
    +--rw remote-address* [address]
    |  +--rw address        inet:ip-address
    |  +--rw port-number?   inet:port-number
    +--rw domain-name?      inet:domain-name
  augment /sys:system/sys-tcs-plus:tacacs-plus/sys-tcs-plus:server
            /sys-tcs-plus:security:
    +--:(tls)
       +--rw client-identity!
       |  +--rw (auth-type)?
       |     +--:(certificate)
       |     |  +--rw certificate
       |     |     +--rw (inline-or-keystore)
       |     |        +--:(inline) {inline-definitions-supported}?
       |     |        |  +--rw inline-definition
       |     |        |     +--rw public-key-format?
       |     |        |     |       identityref
       |     |        |     +--rw public-key?
       |     |        |     |       binary
       |     |        |     +--rw private-key-format?
       |     |        |     |       identityref
       |     |        |     +--rw (private-key-type)
       |     |        |     |  +--:(cleartext-private-key)
       |     |        |     |  |        {cleartext-private-keys}?
       |     |        |     |  |  +--rw cleartext-private-key?
       |     |        |     |  |          binary
       |     |        |     |  +--:(hidden-private-key)
       |     |        |     |  |        {hidden-private-keys}?
       |     |        |     |  |  +--rw hidden-private-key?
       |     |        |     |  |          empty
       |     |        |     |  +--:(encrypted-private-key)
       |     |        |     |           {encrypted-private-keys}?
       |     |        |     |     +--rw encrypted-private-key
       |     |        |     |        +--rw encrypted-by
       |     |        |     |        +--rw encrypted-value-format
       |     |        |     |        |       identityref
       |     |        |     |        +--rw encrypted-value
       |     |        |     |                binary
       |     |        |     +--rw cert-data?
       |     |        |     |       end-entity-cert-cms
       |     |        |     +---n certificate-expiration
       |     |        |     |       {certificate-expiration-\
                                                       notification}?
       |     |        |     |  +-- expiration-date
       |     |        |     |          yang:date-and-time
       |     |        |     +---x generate-csr {csr-generation}?
       |     |        |        +---w input
       |     |        |        |  +---w csr-format    identityref
       |     |        |        |  +---w csr-info      csr-info
       |     |        |        +--ro output
       |     |        |           +--ro (csr-type)
       |     |        |              +--:(p10-csr)
       |     |        |                 +--ro p10-csr?   p10-csr
       |     |        +--:(central-keystore)
       |     |                 {central-keystore-supported,\
                                                    asymmetric-keys}?
       |     |           +--rw central-keystore-reference
       |     |              +--rw asymmetric-key?
       |     |              |       ks:central-asymmetric-key-ref
       |     |              |       {central-keystore-supported,\
                                                    asymmetric-keys}?
       |     |              +--rw certificate?      leafref
       |     +--:(raw-public-key) {tlsc:client-ident-raw-public-key}?
       |     |  +--rw raw-private-key
       |     |     +--rw (inline-or-keystore)
       |     |        +--:(inline) {inline-definitions-supported}?
       |     |        |  +--rw inline-definition
       |     |        |     +--rw public-key-format?
       |     |        |     |       identityref
       |     |        |     +--rw public-key?
       |     |        |     |       binary
       |     |        |     +--rw private-key-format?
       |     |        |     |       identityref
       |     |        |     +--rw (private-key-type)
       |     |        |        +--:(cleartext-private-key)
       |     |        |        |        {cleartext-private-keys}?
       |     |        |        |  +--rw cleartext-private-key?
       |     |        |        |          binary
       |     |        |        +--:(hidden-private-key)
       |     |        |        |        {hidden-private-keys}?
       |     |        |        |  +--rw hidden-private-key?
       |     |        |        |          empty
       |     |        |        +--:(encrypted-private-key)
       |     |        |                 {encrypted-private-keys}?
       |     |        |           +--rw encrypted-private-key
       |     |        |              +--rw encrypted-by
       |     |        |              +--rw encrypted-value-format
       |     |        |              |       identityref
       |     |        |              +--rw encrypted-value
       |     |        |                      binary
       |     |        +--:(central-keystore)
       |     |                 {central-keystore-supported,\
                                                    asymmetric-keys}?
       |     |           +--rw central-keystore-reference?
       |     |                   ks:central-asymmetric-key-ref
       |     +--:(tls13-epsk) {tlsc:client-ident-tls13-epsk}?
       |        +--rw tls13-epsk
       |           +--rw (inline-or-keystore)
       |           |  +--:(inline) {inline-definitions-supported}?
       |           |  |  +--rw inline-definition
       |           |  |     +--rw key-format?
       |           |  |     |       identityref
       |           |  |     +--rw (key-type)
       |           |  |        +--:(cleartext-symmetric-key)
       |           |  |        |  +--rw cleartext-symmetric-key?
       |           |  |        |          binary
       |           |  |        |          {cleartext-symmetric-keys}?
       |           |  |        +--:(hidden-symmetric-key)
       |           |  |        |        {hidden-symmetric-keys}?
       |           |  |        |  +--rw hidden-symmetric-key?
       |           |  |        |          empty
       |           |  |        +--:(encrypted-symmetric-key)
       |           |  |                 {encrypted-symmetric-keys}?
       |           |  |           +--rw encrypted-symmetric-key
       |           |  |              +--rw encrypted-by
       |           |  |              +--rw encrypted-value-format
       |           |  |              |       identityref
       |           |  |              +--rw encrypted-value
       |           |  |                      binary
       |           |  +--:(central-keystore)
       |           |           {central-keystore-supported,symmetric\
                                                              -keys}?
       |           |     +--rw central-keystore-reference?
       |           |             ks:central-symmetric-key-ref
       |           +--rw external-identity                   string
       |           +--rw hash?
       |           |       tlscmn:epsk-supported-hash
       |           +--rw context?                            string
       |           +--rw target-protocol?                    uint16
       |           +--rw target-kdf?                         uint16
       +--rw server-authentication
       |  +--rw ca-certs!
       |  |  +--rw (inline-or-truststore)
       |  |     +--:(inline) {inline-definitions-supported}?
       |  |     |  +--rw inline-definition
       |  |     |     +--rw certificate* [name]
       |  |     |        +--rw name                      string
       |  |     |        +--rw cert-data
       |  |     |        |       trust-anchor-cert-cms
       |  |     |        +---n certificate-expiration
       |  |     |                {certificate-expiration-\
                                                       notification}?
       |  |     |           +-- expiration-date    yang:date-and-time
       |  |     +--:(central-truststore)
       |  |              {central-truststore-supported,certificates}?
       |  |        +--rw central-truststore-reference?
       |  |                ts:central-certificate-bag-ref
       |  +--rw ee-certs!
       |  |  +--rw (inline-or-truststore)
       |  |     +--:(inline) {inline-definitions-supported}?
       |  |     |  +--rw inline-definition
       |  |     |     +--rw certificate* [name]
       |  |     |        +--rw name                      string
       |  |     |        +--rw cert-data
       |  |     |        |       trust-anchor-cert-cms
       |  |     |        +---n certificate-expiration
       |  |     |                {certificate-expiration-\
                                                       notification}?
       |  |     |           +-- expiration-date    yang:date-and-time
       |  |     +--:(central-truststore)
       |  |              {central-truststore-supported,certificates}?
       |  |        +--rw central-truststore-reference?
       |  |                ts:central-certificate-bag-ref
       |  +--rw raw-public-keys! {tlsc:server-auth-raw-public-key}?
       |  |  +--rw (inline-or-truststore)
       |  |     +--:(inline) {inline-definitions-supported}?
       |  |     |  +--rw inline-definition
       |  |     |     +--rw public-key* [name]
       |  |     |        +--rw name                 string
       |  |     |        +--rw public-key-format    identityref
       |  |     |        +--rw public-key           binary
       |  |     +--:(central-truststore)
       |  |              {central-truststore-supported,public-keys}?
       |  |        +--rw central-truststore-reference?
       |  |                ts:central-public-key-bag-ref
       |  +--rw tls13-epsks?       empty
       |          {tlsc:server-auth-tls13-epsk}?
       +--rw hello-params {tlscmn:hello-params}?
       |  +--rw tls-versions
       |  |  +--rw min?   identityref
       |  |  +--rw max?   identityref
       |  +--rw cipher-suites
       |     +--rw cipher-suite*   tlscsa:tls-cipher-suite-algorithm
       +--rw keepalives {tlsc:tls-client-keepalives}?
          +--rw peer-allowed-to-send?   empty
          +--rw test-peer-aliveness!
             +--rw max-wait?       uint16
             +--rw max-attempts?   uint8

The following data nodes are supported:

'remote-address':

Specifies a list of IP address/port numbers that can be used to reach a server instance.

A server instance may be identified by an IPv4 address, IPv6 address, or both.

One or multiple addresses of the same address family may be provided.

The same or distinct port numbers may be used per address family.

This container takes precedence over "address" and "port" data nodes defined in [RFC9105].

'domain-name':

Provides a domain name of the server per Section 3.3 of [I-D.ietf-opsawg-tacacs-tls13].

'client-identity':

Specifies the identity credentials that the client may present when establishing a connection to a server.

'server-authentication':

Specifies how a client authenticate servers.

'hello-params':

Controls TLS versions and cipher suites.

'keepalives':

Providers a set of parameters for testing the aliveness of the server.

4. YANG Module

This module uses types and groupings defined in [RFC6991], [RFC8341], [I-D.ietf-netconf-crypto-types], [I-D.ietf-netconf-trust-anchors], [I-D.ietf-netconf-keystore], and [I-D.ietf-netconf-tls-client-server].

The module augments [RFC9105], which is also an augment of [RFC7317].

The module also cites [RFC9257], [RFC9258], [RFC9258], and [RFC6520].

<CODE BEGINS> file "ietf-system-secure-tacacs@2024-05-23.yang"

=============== NOTE: '\' line wrapping per RFC 8792 ================

module ietf-system-secure-tacacs {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-system-secure-tacacs";
  prefix secure-tacacs;

  import ietf-inet-types {
    prefix inet;
    reference
      "RFC 6991: Common YANG Data Types";
  }
  import ietf-keystore {
    prefix ks;
    reference
      "RFC CCCC: A YANG Data Model for a Keystore";
  }
  import ietf-truststore {
    prefix ts;
    reference
      "RFC BBBB: A YANG Data Model for a Truststore";
  }
  import ietf-tls-client {
    prefix tlsc;
    reference
      "RFC FFFF: YANG Groupings for TLS Clients and TLS Servers";
  }
  import ietf-netconf-acm {
    prefix nacm;
    reference
      "RFC 8341: Network Configuration Access Control Model";
  }
  import ietf-crypto-types {
    prefix ct;
    reference
      "RFC AAAA: YANG Data Types and Groupings for Cryptography";
  }
  import ietf-tls-common {
    prefix tlscmn;
    reference
      "RFC FFFF: YANG Groupings for TLS Clients and TLS Servers";
  }
  import ietf-system {
    prefix sys;
    reference
      "RFC 7317: A YANG Data Model for System Management";
  }
  import ietf-system-tacacs-plus {
    prefix sys-tcs-plus;
    reference
      "RFC 9105: A YANG Data Model for Terminal Access Controller
                 Access-Control System Plus (TACACS+)";
  }

  organization
    "IETF OPSAWG (Operations and Management Area Working Group)";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/opsawg/>
     WG List:  <mailto:opsawg@ietf.org>

     Editor:   Mohamed Boucadair
               <mailto:mohamed.boucadair@orange.com>";
  description
    "This module provides configuration of TACACS+ over TLS
     clients.

     Copyright (c) 2024 IETF Trust and the persons identified as
     authors of the code.  All rights reserved.

     Redistribution and use in source and binary forms, with or
     without modification, is permitted pursuant to, and subject
     to the license terms contained in, the Revised BSD License
     set forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX; see the
     RFC itself for full legal notices.";

  revision 2024-05-23 {
    description
      "Initial revision.";
    reference
      "RFC XXXX: XXXX";
  }

  // to be further tweaked to align with the scope of tacacs+TLS spec
  // can't reuse the groupings in TLS as they are because TLS1.2
  // is not supported
  // can't set a default because of must in a choice

  grouping certificate {
    description
      "Specifies the client identity using a certificate.";
    uses "ks:inline-or-keystore-end-entity-cert-with-key-"
       + "grouping" {
      refine "inline-or-keystore/inline/inline-definition" {
        must 'not(public-key-format) or derived-from-or-self'
           + '(public-key-format, "ct:subject-public-key-'
           + 'info-format")';
      }
      refine "inline-or-keystore/central-keystore/"
           + "central-keystore-reference/asymmetric-key" {
        must 'not(deref(.)/../ks:public-key-format) or '
           + 'derived-from-or-self(deref(.)/../ks:public-'
           + 'key-format, "ct:subject-public-key-info-'
           + 'format")';
      }
    }
  }

  grouping raw-private-key {
    description
      "Specifies the client identity using a raw private
       key.";
    uses ks:inline-or-keystore-asymmetric-key-grouping {
      refine "inline-or-keystore/inline/inline-definition" {
        must 'not(public-key-format) or derived-from-or-self'
           + '(public-key-format, "ct:subject-public-key-'
           + 'info-format")';
      }
      refine "inline-or-keystore/central-keystore/"
           + "central-keystore-reference" {
        must 'not(deref(.)/../ks:public-key-format) or '
           + 'derived-from-or-self(deref(.)/../ks:public-'
           + 'key-format, "ct:subject-public-key-info-format")';
      }
    }
  }

  grouping tls13-epsk {
    description
      "An External Pre-Shared Key (EPSK) is established
       or provisioned out-of-band, i.e., not from a TLS
       connection.  An EPSK is a tuple of (Base Key,
       External Identity, Hash).  When PSKs are provisioned
       out of band, the PSK identity and the KDF hash algorithm
       to be used with the PSK must also be provisioned.";
    reference
      "RFC 8446: The Transport Layer Security (TLS) Protocol
                 Version 1.3, Section 4.2.11
       RFC 9257: Guidance for External Pre-Shared Key (PSK) Usage
                 in TLS, Section 6
       RFC 9258: Importing External Pre-Shared Keys (PSKs) for
                 TLS 1.3, Section 5.1";
    uses ks:inline-or-keystore-symmetric-key-grouping;
    leaf external-identity {
      type string;
      mandatory true;
      description
        "A sequence of bytes used to identify an EPSK. A label for
         a pre-shared key established externally.";
      reference
        "RFC 8446: The Transport Layer Security (TLS) Protocol
                   Version 1.3, Section 4.2.11
         RFC 9257: Guidance for External Pre-Shared Key (PSK)
                   Usage in TLS, Section 4.1";
    }
    leaf hash {
      type tlscmn:epsk-supported-hash;
      default "sha-256";
      description
        "For externally established PSKs, the Hash algorithm must be
         set when the PSK is established or default to SHA-256 if no
         such algorithm is defined.";
      reference
        "RFC 8446: The Transport Layer Security (TLS) Protocol
                   Version 1.3, Section 4.2.11";
    }
    leaf context {
      type string;
      description
        "The context used to determine the EPSK, if any exists. For
         example, context may include information about peer roles or
         identities to mitigate Selfie-style reflection attacks.";
      reference
        "RFC 9258: Importing External Pre-Shared Keys (PSKs) for
                   TLS 1.3, Section 5.1 ";
    }
    leaf target-protocol {
      type uint16;
      description
        "Specifies the protocol for which a PSK is imported for
         use.";
      reference
        "RFC 9258: Importing External Pre-Shared Keys (PSKs) for
                   TLS 1.3, Section 3 ";
    }
    leaf target-kdf {
      type uint16;
      description
        "The KDF for which a PSK is imported for use.";
      reference
        "RFC 9258: Importing External Pre-Shared Keys (PSKs) for
                   TLS 1.3, Section 3";
    }
  }

  grouping client-identity {
    description
      "Identity credentials that the TLS client may present when
       establishing a connection to a TLS server. When configured,
       and requested by the TLS server when establishing a TLS
       session, these credentials are passed in the Certificate
       message.";
    reference
      "RFC 8446: The Transport Layer Security (TLS) Protocol
                 Version 1.3, Section 4.4.2";
    nacm:default-deny-write;
    choice auth-type {
      //default "certificate";
      //mandatory true;
      description
        "A choice amongst authentication types, of which one must
         be enabled and selected.";
      case certificate {
        container certificate {
          description
            "Specifies the client identity using a certificate.";
          uses certificate;
        }
      }
      case raw-public-key {
        if-feature "tlsc:client-ident-raw-public-key";
        container raw-private-key {
          description
            "Specifies the client identity using RPK.";
          uses raw-private-key;
        }
      }
      case tls13-epsk {
        if-feature "tlsc:client-ident-tls13-epsk";
        container tls13-epsk {
          description
            "An EPSK is established or provisioned out-of-band.";
          uses tls13-epsk;
        }
      }
    }
  }

  grouping server-authentication {
    description
      "Specifies how the TLS client can authenticate TLS servers.
       Any combination of credentials is additive and unordered.";
    nacm:default-deny-write;
    container ca-certs {
      presence "Indicates that CA certificates have been configured.
                This statement is present so the mandatory descendant
                nodes do not imply that this node must be
                configured.";
      description
        "A set of CA certificates used by the TLS client to
         authenticate TLS server certificates.
         A server certificate is authenticated if it has a valid
         chain of trust to a configured CA certificate.";
      reference
        "RFC BBBB: A YANG Data Model for a Truststore";
      uses ts:inline-or-truststore-certs-grouping;
    }
    container ee-certs {
      presence "Indicates that EE certificates have been configured.
                This statement is present so the mandatory descendant
                nodes do not imply that this node must be
                configured.";
      description
        "A set of server certificates (i.e., end entity certificates)
         used by the TLS client to authenticate certificates
         presented by TLS servers. A server certificate is
         authenticated if it is an exact match to a configured server
         certificate.";
      reference
        "RFC BBBB: A YANG Data Model for a Truststore";
      uses ts:inline-or-truststore-certs-grouping;
    }
    container raw-public-keys {
      if-feature "tlsc:server-auth-raw-public-key";
      presence "Indicates that raw public keys have been configured.
                This statement is present so the mandatory descendant
                nodes do not imply that this node must be
                configured.";
      description
        "A set of raw public keys used by the TLS client to
         authenticate raw public keys presented by the TLS server.
         A raw public key is authenticated if it is an exact match
         to a configured raw public key.";
      reference
        "RFC BBBB: A YANG Data Model for a Truststore";
      uses ts:inline-or-truststore-public-keys-grouping {
        refine "inline-or-truststore/inline/inline-definition/"
             + "public-key" {
          must 'derived-from-or-self(public-key-format,'
             + ' "ct:subject-public-key-info-format")';
        }
        refine "inline-or-truststore/central-truststore/"
             + "central-truststore-reference" {
          must 'not(deref(.)/../ts:public-key/ts:public-key-'
             + 'format[not(derived-from-or-self(., "ct:subject-'
             + 'public-key-info-format"))])';
        }
      }
    }
    leaf tls13-epsks {
      if-feature "tlsc:server-auth-tls13-epsk";
      type empty;
      description
        "Indicates that the TLS client can authenticate TLS servers
         using configured external PSKs.";
    }
  }

  grouping test-peer-aliveness {
    description
      "Configures the keep-alive policy to proactively test
       the aliveness of the TLS server.  An unresponsive TLS
       server is dropped after approximately max-wait
       * max-attempts seconds.";
    reference
      "RFC 6520: Transport Layer Security (TLS) and Datagram
                 Transport Layer Security (DTLS) Heartbeat
                 Extension";
    leaf max-wait {
      type uint16 {
        range "1..max";
      }
      units "seconds";
      default "30";
      description
        "Sets the amount of time in seconds after which if no data
         has been received from the TLS server, a TLS-level message
         will be sent to test the aliveness of the TLS server.";
    }
    leaf max-attempts {
      type uint8;
      default "3";
      description
        "Sets the maximum number of sequential keep-alive messages
         that can fail to obtain a response from the TLS server
         before assuming the TLS server is no longer alive.";
    }
  }

  grouping hello-params {
    description
      "Configurable parameters for the TLS hello message.";
    nacm:default-deny-write;
    uses tlscmn:hello-params-grouping {
      refine "tls-versions/min" {
        must "not(derived-from-or-self(current(), "
           + "'tlscmn:tls12'))" {
          error-message "TLS 1.2 is not supported as min TLS version\
                                                                  .";
        }
      }
      refine "tls-versions/max" {
        must "not(derived-from-or-self(current(), "
           + "'tlscmn:tls12'))" {
          error-message "TLS 1.2 is not supported as max TLS version\
                                                                  .";
        }
      }
    }
  }

  grouping keepalives {
    description
      "Configures the keepalive policy for the TLS client.";
    nacm:default-deny-write;
    leaf peer-allowed-to-send {
      type empty;
      description
        "Indicates that the remote TLS server is allowed to send
         HeartbeatRequest messages to this TLS client.";
      reference
        "RFC 6520: Transport Layer Security (TLS) and Datagram
                   Transport Layer Security (DTLS) Heartbeat
                   Extension";
    }
    container test-peer-aliveness {
      presence "Indicates that the TLS client proactively tests the
                aliveness of the remote TLS server.";
      description
        "Configures the keep-alive policy to proactively test the
         aliveness of the TLS server.  An unresponsive TLS server is
         dropped after approximately max-wait * max-attempts
         seconds.";
      uses test-peer-aliveness;
    }
  }

  grouping tls-client {
    description
      "A grouping for configuring a TLS client without any
       consideration for how an underlying TCP session is
       established.";
    container client-identity {
      presence
        "Indicates that a TLS-level client identity has been
         configured.
         This statement is present so the mandatory descendant do not
         imply that this node must be configured.";
      description
        "Identity credentials the TLS client may present when
         establishing a connection to a TLS server.";
      uses client-identity;
    }
    container server-authentication {
      must 'ca-certs or ee-certs or raw-public-keys or tls13-epsks';
      description
        "Specifies how the TLS client can authenticate TLS servers.";
      uses server-authentication;
    }
    container hello-params {
      if-feature "tlscmn:hello-params";
      description
        "Configurable parameters for the TLS hello message.";
      uses hello-params;
    }
    container keepalives {
      if-feature "tlsc:tls-client-keepalives";
      description
        "Configures the keepalive policy for the TLS client.";
      uses keepalives;
    }
  }

  grouping tcp-server-info {
    description
      "A grouping for configuring the information to contact
       a TCP server.";
    list remote-address {
      key "address";
      description
        "A server instance may be reachable using multiple IP address
         and port numbers. For example, use the same port number in
         different address families or different port numbers in the
         same address family.";
      leaf address {
        type inet:ip-address;
        description
          "The remote IP address to reach a server.";
      }
      leaf port-number {
        type inet:port-number;
        description
          "The remote port number of the server.";
      }
    }
  }

  augment "/sys:system/sys-tcs-plus:tacacs-plus"
        + "/sys-tcs-plus:server" {
    description
      "Adds server's domain name.";
    uses tcp-server-info {
      refine "remote-address/address" {
        must 'not(../../sys-tcs-plus:address)' {
          error-message
            "Either use the list of bind points or RFC 9105 address
             data node, not both.";
        }
      }
      refine "remote-address/port-number" {
        must 'not(../../sys-tcs-plus:port)' {
          error-message
            "Either use the list of bind points or RFC 9105 port
             data node, not both.";
        }
        default "1234"; // to be replaced by TACACS-TLS-PORT
      }
    }
    leaf domain-name {
      type inet:domain-name;
      description
        "Provides a domain name of the TACACS+ server.";
    }
  }

  augment
    "/sys:system/sys-tcs-plus:tacacs-plus/sys-tcs-plus:server"
  + "/sys-tcs-plus:security" {
    description
      "Adds TLS case.";
    case tls {
      description
        "TLS is used.";
      uses tls-client;
    }
  }
}

<CODE ENDS>

5. Security Considerations

This section uses the template described in Section 3.7 of [I-D.ietf-netmod-rfc8407bis].

The YANG module specified in this document defines schema for data that is designed to be accessed via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446].

The Network Configuration Access Control Model (NACM) [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content.

There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) and delete operations to these data nodes without proper protection or authentication can have a negative effect on network operations. Specifically, the following subtrees and data nodes have particular sensitivities/vulnerabilities:

 'xxx':
 :  xxxx.

Some of the readable data nodes in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to these data nodes. Specifically, the following subtrees and data nodes have particular sensitivities/vulnerabilities:

 'xxx':
 :  xxxx.

This YANG module uses groupings from other YANG modules that define nodes that may be considered sensitive or vulnerable in network environments. Refer to Section 5.3 of [I-D.ietf-netconf-tls-client-server] for information as to which nodes may be considered sensitive or vulnerable in network environments.

6. IANA Considerations

IANA is requested to register the following URI in the "ns" subregistry within the "IETF XML Registry" [RFC3688]:

   URI:  urn:ietf:params:xml:ns:yang:ietf-system-secure-tacacs
   Registrant Contact:  The IESG.
   XML:  N/A; the requested URI is an XML namespace.

IANA is requested to register the following YANG module in the "YANG Module Names" registry [RFC6020] within the "YANG Parameters" registry group:

   Name:  ietf-system-secure-tacacs
   Namespace:  urn:ietf:params:xml:ns:yang:ietf-system-secure-tacacs
   Prefix:  secure-tacacs
   Maintained by IANA?  N
   Reference:  RFC XXXX

7. References

7.1. Normative References

[I-D.ietf-netconf-crypto-types]
Watsen, K., "YANG Data Types and Groupings for Cryptography", Work in Progress, Internet-Draft, draft-ietf-netconf-crypto-types-34, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-crypto-types-34>.
[I-D.ietf-netconf-keystore]
Watsen, K., "A YANG Data Model for a Keystore and Keystore Operations", Work in Progress, Internet-Draft, draft-ietf-netconf-keystore-35, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-keystore-35>.
[I-D.ietf-netconf-tls-client-server]
Watsen, K., "YANG Groupings for TLS Clients and TLS Servers", Work in Progress, Internet-Draft, draft-ietf-netconf-tls-client-server-41, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-tls-client-server-41>.
[I-D.ietf-netconf-trust-anchors]
Watsen, K., "A YANG Data Model for a Truststore", Work in Progress, Internet-Draft, draft-ietf-netconf-trust-anchors-28, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-trust-anchors-28>.
[I-D.ietf-opsawg-tacacs-tls13]
Dahm, T., Heasley, J., dcmgash@cisco.com, and A. Ota, "Terminal Access Controller Access-Control System Plus (TACACS+) over TLS 1.3", Work in Progress, Internet-Draft, draft-ietf-opsawg-tacacs-tls13-10, , <https://datatracker.ietf.org/doc/html/draft-ietf-opsawg-tacacs-tls13-10>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC3688]
Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <https://www.rfc-editor.org/rfc/rfc3688>.
[RFC6020]
Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, , <https://www.rfc-editor.org/rfc/rfc6020>.
[RFC6241]
Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, , <https://www.rfc-editor.org/rfc/rfc6241>.
[RFC6242]
Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, , <https://www.rfc-editor.org/rfc/rfc6242>.
[RFC6520]
Seggelmann, R., Tuexen, M., and M. Williams, "Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) Heartbeat Extension", RFC 6520, DOI 10.17487/RFC6520, , <https://www.rfc-editor.org/rfc/rfc6520>.
[RFC6991]
Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, , <https://www.rfc-editor.org/rfc/rfc6991>.
[RFC7317]
Bierman, A. and M. Bjorklund, "A YANG Data Model for System Management", RFC 7317, DOI 10.17487/RFC7317, , <https://www.rfc-editor.org/rfc/rfc7317>.
[RFC8040]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <https://www.rfc-editor.org/rfc/rfc8040>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8341]
Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, , <https://www.rfc-editor.org/rfc/rfc8341>.
[RFC8446]
Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, , <https://www.rfc-editor.org/rfc/rfc8446>.
[RFC9105]
Wu, B., Ed., Zheng, G., and M. Wang, Ed., "A YANG Data Model for Terminal Access Controller Access-Control System Plus (TACACS+)", RFC 9105, DOI 10.17487/RFC9105, , <https://www.rfc-editor.org/rfc/rfc9105>.
[RFC9257]
Housley, R., Hoyland, J., Sethi, M., and C. A. Wood, "Guidance for External Pre-Shared Key (PSK) Usage in TLS", RFC 9257, DOI 10.17487/RFC9257, , <https://www.rfc-editor.org/rfc/rfc9257>.
[RFC9258]
Benjamin, D. and C. A. Wood, "Importing External Pre-Shared Keys (PSKs) for TLS 1.3", RFC 9258, DOI 10.17487/RFC9258, , <https://www.rfc-editor.org/rfc/rfc9258>.

7.2. Informative References

[I-D.ietf-netmod-rfc8407bis]
Bierman, A., Boucadair, M., and Q. Wu, "Guidelines for Authors and Reviewers of Documents Containing YANG Data Models", Work in Progress, Internet-Draft, draft-ietf-netmod-rfc8407bis-11, , <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-rfc8407bis-11>.
[RFC8340]
Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, , <https://www.rfc-editor.org/rfc/rfc8340>.
[RFC8907]
Dahm, T., Ota, A., Medway Gash, D.C., Carrel, D., and L. Grant, "The Terminal Access Controller Access-Control System Plus (TACACS+) Protocol", RFC 8907, DOI 10.17487/RFC8907, , <https://www.rfc-editor.org/rfc/rfc8907>.

Acknowledgments

The document leverages data structures defined in [I-D.ietf-netconf-tls-client-server].

Author's Address

Mohamed Boucadair (editor)
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