Add device agent library

Provide enrollment, elevated install, posture checks, keystore, and
system-tray helpers shared by the probo-agent binary.

Signed-off-by: Ludovic Vielle <ludovic@probo.com>

pkg/deviceagent/enroll.go

@@ -0,0 +1,117 @@
+// Copyright (c) 2026 Probo Inc <hello@probo.com>.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+package deviceagent
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+)
+
+// ErrServerURLMismatch is returned when install is re-run with a --server
+// that differs from the persisted config.
+var ErrServerURLMismatch = errors.New("server URL does not match persisted config; uninstall first")
+
+// LoadOrExchangeAPIKey returns a persisted API key for install.
+// If agent.key already exists, it is returned without contacting the server
+// only when serverURL matches the server_url persisted in config.json.
+// Otherwise the enrollment token is exchanged, the key and server binding
+// are saved to disk immediately, and then the key is returned.
+func LoadOrExchangeAPIKey(
+	ctx context.Context,
+	dir string,
+	client *Client,
+	serverURL string,
+	enrollmentToken string,
+) (string, error) {
+	normalized, err := NormalizeServerURL(serverURL)
+	if err != nil {
+		return "", fmt.Errorf("invalid server URL: %w", err)
+	}
+
+	apiKey, err := LoadAPIKey(dir)
+	if err == nil {
+		if err := validatePersistedServerURL(dir, normalized); err != nil {
+			return "", err
+		}
+
+		return apiKey, nil
+	}
+
+	if !errors.Is(err, ErrKeyNotFound) {
+		return "", fmt.Errorf("cannot load device api key: %w", err)
+	}
+
+	apiKey, err = client.ExchangeEnrollmentToken(ctx, enrollmentToken)
+	if err != nil {
+		return "", fmt.Errorf("cannot exchange enrollment token: %w", err)
+	}
+
+	if err := SaveAPIKey(dir, apiKey); err != nil {
+		return "", fmt.Errorf("cannot save device api key: %w", err)
+	}
+
+	if err := SaveConfig(dir, &Config{ServerURL: normalized}); err != nil {
+		if delErr := DeleteAPIKey(dir); delErr != nil {
+			return "", fmt.Errorf(
+				"cannot save device config: %w (also cannot delete device api key: %v)",
+				err,
+				delErr,
+			)
+		}
+
+		return "", fmt.Errorf("cannot save device config: %w", err)
+	}
+
+	return apiKey, nil
+}
+
+func validatePersistedServerURL(dir, serverURL string) error {
+	normalized, err := NormalizeServerURL(serverURL)
+	if err != nil {
+		return fmt.Errorf("invalid server URL: %w", err)
+	}
+
+	cfg, err := LoadConfig(dir)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return ErrServerURLMismatch
+		}
+
+		return fmt.Errorf("cannot load device config: %w", err)
+	}
+
+	if cfg.ServerURL == "" {
+		return ErrServerURLMismatch
+	}
+
+	persisted, err := NormalizeServerURL(cfg.ServerURL)
+	if err != nil {
+		return fmt.Errorf("invalid persisted server URL: %w", err)
+	}
+
+	if persisted != normalized {
+		return ErrServerURLMismatch
+	}
+
+	return nil
+}