module ietf-ssh-client {

    yang-version 1.1;

    namespace
      "urn:ietf:params:xml:ns:yang:ietf-ssh-client";

    prefix sshc;

    import ietf-netconf-acm {
      prefix nacm;
      reference
        "RFC 8341: Network Configuration Access Control Model";


    }
    import ietf-crypto-types {
      prefix ct;
      reference
        "RFC 9640: YANG Data Types and Groupings for Cryptography";


    }
    import ietf-truststore {
      prefix ts;
      reference
        "RFC 9641: A YANG Data Model for a Truststore";


    }
    import ietf-keystore {
      prefix ks;
      reference
        "RFC 9642: A YANG Data Model for a Keystore";


    }
    import ietf-ssh-common {
      prefix sshcmn;
      reference
        "RFC 9644: YANG Groupings for SSH Clients and SSH Servers";


    }

    organization
      "IETF NETCONF (Network Configuration) Working Group";

    contact
      "WG Web:   https://datatracker.ietf.org/wg/netconf
     WG List:  NETCONF WG list <mailto:netconf@ietf.org>
     Author:   Kent Watsen <mailto:kent+ietf@watsen.net>";

    description
      "This module defines a reusable grouping for SSH clients that
     can be used as a basis for specific SSH client instances.

     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 (RFC 2119)
     (RFC 8174) when, and only when, they appear in all
     capitals, as shown here.

     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 9644
     (https://www.rfc-editor.org/info/rfc9644); see the RFC
     itself for full legal notices.";

    revision "2024-10-10" {
      description "Initial version.";
      reference
        "RFC 9644: YANG Groupings for SSH Clients and SSH Servers";

    }


    feature ssh-client-keepalives {
      description
        "SSH keepalive parameters are configurable for
       SSH clients on the server implementing this feature.";
    }

    feature client-ident-publickey {
      description
        "Indicates that the 'publickey' authentication type, per
       RFC 4252, is supported for client identification.
       The 'publickey' authentication type is required by
       RFC 4252, but common implementations allow it to
       be disabled.";
      reference
        "RFC 4252:
         The Secure Shell (SSH) Authentication Protocol";

    }

    feature client-ident-password {
      description
        "Indicates that the 'password' authentication type, per
       RFC 4252, is supported for client identification.";
      reference
        "RFC 4252:
         The Secure Shell (SSH) Authentication Protocol";

    }

    feature client-ident-hostbased {
      description
        "Indicates that the 'hostbased' authentication type, per
       RFC 4252, is supported for client identification.";
      reference
        "RFC 4252:
         The Secure Shell (SSH) Authentication Protocol";

    }

    feature client-ident-none {
      description
        "Indicates that the 'none' authentication type, per
       RFC 4252, is supported for client identification.
       It is NOT RECOMMENDED to enable this feature.";
      reference
        "RFC 4252:
         The Secure Shell (SSH) Authentication Protocol";

    }

    grouping ssh-client-grouping {
      description
        "A reusable grouping for configuring an SSH client without
       any consideration for how an underlying TCP session is
       established.

       Note that this grouping uses fairly typical descendant
       node names such that a nesting of 'uses' statements will
       have name conflicts.  It is intended that the consuming
       data model will resolve the issue (e.g., by wrapping
       the 'uses' statement in a container called
       'ssh-client-parameters').  This model purposely does
       not do this itself so as to provide maximum flexibility
       to consuming models.";
      container client-identity {
        nacm:default-deny-write;
        description
          "The username and authentication methods for the client.
         The authentication methods are unordered.  Clients may
         initially send any configured method or, per Section 5.2 of
         RFC 4252, send the 'none' method to prompt the server
         to provide a list of productive methods.  Whenever a
         choice amongst methods arises, implementations SHOULD
         use a default ordering that prioritizes automation
         over human interaction.";
        leaf username {
          type string;
          description
            "The username of this user.  This will be the username
           used, for instance, to log into an SSH server.";
        }

        container public-key {
          if-feature client-ident-publickey;
          presence
            "Indicates that public-key-based authentication has been
           configured.  This statement is present so the mandatory
           descendant nodes do not imply that this node must be
           configured.";
          description
            "A locally defined or referenced asymmetric key
           pair to be used for client identification.";
          reference
            "RFC 9642: A YANG Data Model for a Keystore";

          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:ssh-public-key-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:ssh-public-key-format")';
            }
          }
        }  // container public-key

        container password {
          if-feature client-ident-password;
          presence
            "Indicates that password-based authentication has been
           configured.  This statement is present so the mandatory
           descendant nodes do not imply that this node must be
           configured.";
          description
            "A password to be used to authenticate the client's
           identity.";
          uses ct:password-grouping;
        }  // container password

        container hostbased {
          if-feature client-ident-hostbased;
          presence
            "Indicates that host-based authentication is configured.
           This statement is present so the mandatory descendant
           nodes do not imply that this node must be configured.";
          description
            "A locally defined or referenced asymmetric key
           pair to be used for host identification.";
          reference
            "RFC 9642: A YANG Data Model for a Keystore";

          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:ssh-public-key-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:ssh-public-key-format")';
            }
          }
        }  // container hostbased

        leaf none {
          if-feature client-ident-none;
          type empty;
          description
            "Indicates that the 'none' algorithm is used for client
           identification.";
        }

        container certificate {
          if-feature sshcmn:ssh-x509-certs;
          presence
            "Indicates that certificate-based authentication has been
           configured.  This statement is present so the mandatory
           descendant nodes do not imply that this node must be
           configured.";
          description
            "A locally defined or referenced certificate
           to be used for client identification.";
          reference
            "RFC 9642: A YANG Data Model for a Keystore";

          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")';
            }
          }
        }  // container certificate
      }  // container client-identity

      container server-authentication {
        nacm:default-deny-write;
        must
          'ssh-host-keys or ca-certs or ee-certs';
        description
          "Specifies how the SSH client can authenticate SSH servers.
         Any combination of authentication methods is additive and
         unordered.";
        container ssh-host-keys {
          presence
            "Indicates that the SSH host key have been configured.
           This statement is present so the mandatory descendant
           nodes do not imply that this node must be configured.";
          description
            "A bag of SSH host keys used by the SSH client to
           authenticate SSH server host keys.  A server host key
           is authenticated if it is an exact match to a
           configured SSH host key.";
          reference
            "RFC 9641: 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:ssh-public-key-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:ssh-'
                  + 'public-key-format"))])';
            }
          }
        }  // container ssh-host-keys

        container ca-certs {
          if-feature sshcmn:ssh-x509-certs;
          presence
            "Indicates that the 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 Certification Authority (CA) certificates used by
           the SSH client to authenticate SSH servers.  A server
           is authenticated if its certificate has a valid chain
           of trust to a configured CA certificate.";
          reference
            "RFC 9641: A YANG Data Model for a Truststore";

          uses ts:inline-or-truststore-certs-grouping;
        }  // container ca-certs

        container ee-certs {
          if-feature sshcmn:ssh-x509-certs;
          presence
            "Indicates that the 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 end-entity (EE) certificates used by the SSH
           client to authenticate SSH servers.  A server is
           authenticated if its certificate is an exact match to a
           configured end-entity certificate.";
          reference
            "RFC 9641: A YANG Data Model for a Truststore";

          uses ts:inline-or-truststore-certs-grouping;
        }  // container ee-certs
      }  // container server-authentication

      container transport-params {
        nacm:default-deny-write;
        if-feature sshcmn:transport-params;
        description
          "Configurable parameters of the SSH transport layer.";
        uses sshcmn:transport-params-grouping;
      }  // container transport-params

      container keepalives {
        nacm:default-deny-write;
        if-feature ssh-client-keepalives;
        presence
          "Indicates that the SSH client proactively tests the
         aliveness of the remote SSH server.";
        description
          "Configures the keepalive policy to proactively test
         the aliveness of the SSH server.  An unresponsive SSH
         server is dropped after approximately max-wait *
         max-attempts seconds.  Per Section 4 of RFC 4254,
         the SSH client SHOULD send an SSH_MSG_GLOBAL_REQUEST
         message with a purposely nonexistent 'request name'
         value (e.g., keepalive@example.com) and the 'want reply'
         value set to '1'.";
        reference
          "RFC 4254: The Secure Shell (SSH) Connection Protocol";

        leaf max-wait {
          type uint16 {
            range "1..max";
          }
          units "seconds";
          default "30";
          description
            "Sets the amount of time in seconds after which an
           SSH-level message will be sent to test the aliveness
           of the SSH server if no data has been received from the
           SSH server.";
        }

        leaf max-attempts {
          type uint8;
          default "3";
          description
            "Sets the maximum number of sequential keepalive
           messages that can fail to obtain a response from
           the SSH server before assuming the SSH server is
           no longer alive.";
        }
      }  // container keepalives
    }  // grouping ssh-client-grouping
  }  // module ietf-ssh-client