charon-cmd: Add --agent option to authenticate using ssh-agent(1)

The socket path is read from the SSH_AUTH_SOCK environment variable.
So using this with sudo might require the -E command line (or an appropriate
sudoers config) to preserve the environment.

src/charon-cmd/cmd/cmd_connection.c

@@ -387,6 +387,7 @@ METHOD(cmd_connection_t, handle, bool,
 			this->identity = arg;
 			break;
 		case CMD_OPT_RSA:
+		case CMD_OPT_AGENT:
 			this->key_seen = TRUE;
 			break;
 		case CMD_OPT_LOCAL_TS:

src/charon-cmd/cmd/cmd_creds.c

@@ -47,6 +47,16 @@ struct private_cmd_creds_t {
 	 * Already prompted for password?
 	 */
 	bool prompted;
+
+	/**
+	 * Provide keys via ssh-agent
+	 */
+	bool agent;
+
+	/**
+	 * Local identity
+	 */
+	char *identity;
 };
 
 /**
@@ -119,6 +129,54 @@ static void load_key(private_cmd_creds_t *this, key_type_t type, char *path)
 	this->creds->add_key(this->creds, privkey);
 }
 
+/**
+ * Load a private and public key via ssh-agent
+ */
+static void load_agent(private_cmd_creds_t *this)
+{
+	private_key_t *privkey;
+	public_key_t *pubkey;
+	identification_t *id;
+	certificate_t *cert;
+	char *agent;
+
+	agent = getenv("SSH_AUTH_SOCK");
+	if (!agent)
+	{
+		DBG1(DBG_CFG, "ssh-agent socket not found");
+		exit(1);
+	}
+
+	privkey = lib->creds->create(lib->creds, CRED_PRIVATE_KEY,
+								 KEY_RSA, BUILD_AGENT_SOCKET, agent, BUILD_END);
+	if (!privkey)
+	{
+		DBG1(DBG_CFG, "failed to load private key from ssh-agent");
+		exit(1);
+	}
+	pubkey = privkey->get_public_key(privkey);
+	if (!pubkey)
+	{
+		DBG1(DBG_CFG, "failed to load public key from ssh-agent");
+		privkey->destroy(privkey);
+		exit(1);
+	}
+	id = identification_create_from_string(this->identity);
+	cert = lib->creds->create(lib->creds, CRED_CERTIFICATE,
+							  CERT_TRUSTED_PUBKEY, BUILD_PUBLIC_KEY, pubkey,
+							  BUILD_SUBJECT, id, BUILD_END);
+	pubkey->destroy(pubkey);
+	id->destroy(id);
+	if (!cert)
+	{
+		DBG1(DBG_CFG, "failed to create certificate for ssh-agent public key");
+		privkey->destroy(privkey);
+		exit(1);
+	}
+	this->creds->add_cert(this->creds, TRUE, cert);
+	this->creds->add_key(this->creds, privkey);
+}
+
 METHOD(cmd_creds_t, handle, bool,
 	private_cmd_creds_t *this, cmd_option_type_t opt, char *arg)
 {
@@ -130,9 +188,19 @@ METHOD(cmd_creds_t, handle, bool,
 		case CMD_OPT_RSA:
 			load_key(this, KEY_RSA, arg);
 			break;
+		case CMD_OPT_IDENTITY:
+			this->identity = arg;
+			break;
+		case CMD_OPT_AGENT:
+			this->agent = TRUE;
+			break;
 		default:
 			return FALSE;
 	}
+	if (this->agent && this->identity)
+	{
+		load_agent(this);
+	}
 	return TRUE;
 }
 

src/charon-cmd/cmd/cmd_options.c

@@ -35,6 +35,8 @@ cmd_option_t cmd_options[CMD_OPT_COUNT] = {
 	  "trusted certificate, for authentication or trust chain validation" },
 	{ CMD_OPT_RSA, "rsa", required_argument, "path",
 	  "RSA private key to use for authentication" },
+	{ CMD_OPT_AGENT, "agent", no_argument, "",
+	  "use SSH agent for authentication"},
 	{ CMD_OPT_LOCAL_TS, "local-ts", required_argument, "subnet",
 	  "additional traffic selector to propose for our side" },
 	{ CMD_OPT_REMOTE_TS, "remote-ts", required_argument, "subnet",

src/charon-cmd/cmd/cmd_options.h

@@ -35,6 +35,7 @@ enum cmd_option_type_t {
 	CMD_OPT_REMOTE_IDENTITY,
 	CMD_OPT_CERT,
 	CMD_OPT_RSA,
+	CMD_OPT_AGENT,
 	CMD_OPT_LOCAL_TS,
 	CMD_OPT_REMOTE_TS,
 	CMD_OPT_PROFILE,