How to Authenticate to SSH with a PEM/Key in Go?

Authenticating to SSH with a pem/Key in Go

Connecting to a remote SSH server using a private key can be a convenient way to automate tasks and manage resources. The Go programming language offers the ssh package, which provides support for establishing SSH connections. However, the documentation can be somewhat unclear regarding how to authenticate with a private key.

To connect to a server using SSH with a pem key, you can follow these steps:

1. Obtain a Signer: You need to obtain a ssh.Signer from your private key. This can be done using the ssh.ParsePrivateKey function or the ssh.NewSignerFromKey function for specific key types (e.g., rsa, dsa, ecdsa).
2. Create an AuthMethod: Convert the Signer object into an ssh.AuthMethod using the ssh.PublicKeys function. This wraps the Signer and allows it to be used for authentication during the SSH connection.
3. Configure ClientConfig: Set up an ssh.ClientConfig object that includes your authentication method, username, and any other necessary configuration parameters.
4. Dial the Connection: Use the ssh.Dial function to establish a connection to the remote server using your ClientConfig.
5. Create a Session: Once the connection is established, create a ssh.Session to execute commands on the remote server.

Example:

<code class="go">package main

import (
    "crypto/x509"
    "fmt"
    "io/ioutil"
    "log"
    "net"
    "os"

    "golang.org/x/crypto/ssh"
)

func main() {
    // Parse the private key
    key, err := ioutil.ReadFile("mykey.pem")
    if err != nil {
        log.Fatal(err)
    }

    // Get the signer
    signer, err := ssh.ParsePrivateKey(key)
    if err != nil {
        log.Fatal(err)
    }

    // Switch to using an agent if SSH_AUTH_SOCK is set
    if authSock := os.Getenv("SSH_AUTH_SOCK"); authSock != "" {
        sock, err := net.Dial("unix", authSock)
        if err != nil {
            log.Fatalf("Failed to connect to agent: %v", err)
        }
        _ = sock
        // TODO(harsh)
        // Implement working with agent.
    }

    // Create the AuthMethod
    authMethods := []ssh.AuthMethod{ssh.PublicKeys(signer)}

    // Set up the ClientConfig
    clientConfig := &ssh.ClientConfig{
        User:            "username",
        Auth:            authMethods,
        HostKeyCallback: ssh.InsecureIgnoreHostKey(),
    }

    // Dial the connection
    client, err := ssh.Dial("tcp", "aws-hostname:22", clientConfig)
    if err != nil {
        log.Fatal(err)
    }

    // Create a session
    session, err := client.NewSession()
    if err != nil {
        log.Fatal(err)
    }

    // Execute a command
    output, err := session.Output("whoami")
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println("Output:", string(output))

    // Close the session and client
    _ = session.Close()
    _ = client.Close()
}</code>

By following these steps, you can establish a secure SSH connection using a private key and execute commands on the remote server using the Go standard library's ssh package.

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