HostKeeper/pkg/ssh/auth.go

package ssh

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"

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

// getAuthMethods returns SSH authentication methods based on host config
func (c *Client) getAuthMethods() ([]cryptossh.AuthMethod, error) {
	var authMethods []cryptossh.AuthMethod

	switch c.host.Auth.Type {
	case "password":
		if c.host.Auth.Password == "" {
			return nil, fmt.Errorf("password auth requires password")
		}
		authMethods = append(authMethods, cryptossh.Password(c.host.Auth.Password))

	case "key":
		signer, err := c.getKeySigner()
		if err != nil {
			return nil, fmt.Errorf("failed to setup key authentication: %w", err)
		}
		authMethods = append(authMethods, cryptossh.PublicKeys(signer))

	case "both":
		// Try password first
		if c.host.Auth.Password != "" {
			authMethods = append(authMethods, cryptossh.Password(c.host.Auth.Password))
		}
		// Then try key
		signer, err := c.getKeySigner()
		if err == nil {
			authMethods = append(authMethods, cryptossh.PublicKeys(signer))
		}

	default:
		return nil, fmt.Errorf("unsupported authentication type: %s", c.host.Auth.Type)
	}

	if len(authMethods) == 0 {
		return nil, fmt.Errorf("no authentication methods configured")
	}

	return authMethods, nil
}

// getKeySigner returns an SSH signer for key-based authentication
//
// Phase 1: Loads key from KeyID as a file path, or from common SSH key locations
// Phase 2: Will integrate with the storage layer for encrypted key storage
func (c *Client) getKeySigner() (cryptossh.Signer, error) {
	var keyPath string

	if c.host.Auth.KeyID != "" {
		// If KeyID looks like a path, use it directly
		if strings.HasPrefix(c.host.Auth.KeyID, "/") || strings.HasPrefix(c.host.Auth.KeyID, "~") {
			keyPath = expandPath(c.host.Auth.KeyID)
		} else {
			// Try ~/.ssh/<keyID>
			home, err := os.UserHomeDir()
			if err != nil {
				return nil, fmt.Errorf("failed to get home directory: %w", err)
			}
			keyPath = filepath.Join(home, ".ssh", c.host.Auth.KeyID)
		}
	} else {
		// Fall back to default key locations
		keyPath = getDefaultKeyPath()
	}

	// Read the key file
	keyData, err := os.ReadFile(keyPath) //nolint:gosec
	if err != nil {
		return nil, fmt.Errorf("failed to read key file %s: %w", keyPath, err)
	}

	// Parse the key (support passphrase-protected keys in Phase 2)
	var signer cryptossh.Signer
	if c.host.Auth.Password != "" {
		signer, err = cryptossh.ParsePrivateKeyWithPassphrase(keyData, []byte(c.host.Auth.Password))
	} else {
		signer, err = cryptossh.ParsePrivateKey(keyData)
	}
	if err != nil {
		return nil, fmt.Errorf("failed to parse private key: %w", err)
	}

	return signer, nil
}

// getDefaultKeyPath returns the first existing default SSH key path
func getDefaultKeyPath() string {
	home, err := os.UserHomeDir()
	if err != nil {
		return ""
	}

	candidates := []string{
		"id_ed25519",
		"id_rsa",
		"id_ecdsa",
		"id_dsa",
	}

	for _, name := range candidates {
		path := filepath.Join(home, ".ssh", name)
		if _, err := os.Stat(path); err == nil {
			return path
		}
	}

	return ""
}

// expandPath expands ~ to the home directory
func expandPath(path string) string {
	if strings.HasPrefix(path, "~/") {
		home, err := os.UserHomeDir()
		if err == nil {
			return filepath.Join(home, path[2:])
		}
	}
	return path
}