ProxyJump

+-----------+      +----------------------+      +---------------------+
| Local app | ---> | Jump host            | ---> | Final SSH server    |
+-----------+      +----------------------+      +---------------------+
                     | 1. Authenticate here |
                     | 2. Open direct-tcpip |
                     |    to the next hop   |
                     +----------------------+

What actually happens:

1. SSH connection #1 is established to the jump host
2. A direct-tcpip channel is opened through that jump host
3. SSH connection #2 is established inside that channel
4. The returned SSHConnection is the final target connection

import Traversio

let configuration = SSHClientConfiguration(
    host: "db-admin.internal",
    username: "deploy",
    authentication: .password("final-target-password"),
    hostKeyPolicy: .knownHostsFile("/Users/me/.ssh/known_hosts"),
    compressionPreference: .delayedZlib,
    proxyJumpHosts: [
        SSHProxyJumpHost(
            host: "bastion.example.com",
            username: "deploy",
            authentication: .password("bastion-password"),
            hostKeyPolicy: .knownHostsFile("/Users/me/.ssh/known_hosts"),
            compressionPreference: .delayedZlib
        )
    ]
)

let result = try await SSHClient.withConnection(configuration: configuration) { connection in
    try await connection.execute("hostname")
}

let configuration = SSHClientConfiguration(
    host: "final.internal",
    username: "deploy",
    authentication: .password("final-password"),
    hostKeyPolicy: .acceptAnyVerifiedHostKey,
    proxyJumpHosts: [
        SSHProxyJumpHost(
            host: "bastion-a.example.com",
            username: "jump-a",
            authentication: .password("jump-a-password"),
            hostKeyPolicy: .acceptAnyVerifiedHostKey
        ),
        SSHProxyJumpHost(
            host: "bastion-b.internal",
            username: "jump-b",
            authentication: .password("jump-b-password"),
            hostKeyPolicy: .acceptAnyVerifiedHostKey
        ),
    ]
)