feat: add ssh-agent authentication method support (#10)

README.md

@@ -26,6 +26,7 @@ tunnel := sshtunnel.NewSSHTunnel(
    // Pick ONE of the following authentication methods:
    sshtunnel.PrivateKeyFile("path/to/private/key.pem"), // 1. private key
    ssh.Password("password"),                            // 2. password
+   sshtunnel.SSHAgent(),                                // 3. ssh-agent
 
    // The destination host and port of the actual server.
    "dqrsdfdssdfx.us-east-1.redshift.amazonaws.com:5439",

ssh_agent.go

@@ -0,0 +1,16 @@
+package sshtunnel
+
+import (
+	"net"
+	"os"
+
+	"golang.org/x/crypto/ssh"
+	"golang.org/x/crypto/ssh/agent"
+)
+
+func SSHAgent() ssh.AuthMethod {
+	if sshAgent, err := net.Dial("unix", os.Getenv("SSH_AUTH_SOCK")); err == nil {
+		return ssh.PublicKeysCallback(agent.NewClient(sshAgent).Signers)
+	}
+	return nil
+}