Extract AppAPI auth and OCS preferences from CheckDNS.

Publish gonexapp v1 with Credentials, OCSClient, and parameterized
AppAPIPreferences so ExApps share Nextcloud ExApp plumbing per ADR 0013.

Co-authored-by: Cursor <cursoragent@cursor.com>

preferences.go

@@ -0,0 +1,93 @@
+package gonexapp
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+)
+
+// AppAPIPreferences reads and writes one string ExApp preference for the requesting user.
+type AppAPIPreferences struct {
+	Cred   Credentials
+	AppID  string
+	Key    string
+	Client *http.Client
+	OCS    OCSClient
+}
+
+// NewAppAPIPreferences returns a preference store for appID and key using cred for auth.
+func NewAppAPIPreferences(cred Credentials, appID, key string) AppAPIPreferences {
+	return AppAPIPreferences{
+		Cred:  cred,
+		AppID: appID,
+		Key:   key,
+		OCS:   OCSClient{Cred: cred},
+	}
+}
+
+func (p AppAPIPreferences) ocsClient() OCSClient {
+	c := p.OCS
+	if c.Cred.BaseURL == "" {
+		c.Cred = p.Cred
+	}
+	if c.Client == nil {
+		c.Client = p.Client
+	}
+	return c
+}
+
+// Get loads the configured preference key for the requesting user.
+func (p AppAPIPreferences) Get() (string, error) {
+	ocs := p.ocsClient()
+	body, _ := json.Marshal(map[string]any{"configKeys": []string{p.Key}})
+	raw, err := ocs.Call(http.MethodPost, "apps/app_api/api/v1/ex-app/preference/get-values", body)
+	if err != nil {
+		return "", err
+	}
+	return decodePreferenceValue(raw, p.Key)
+}
+
+// Set stores value for the configured preference key.
+func (p AppAPIPreferences) Set(value string) error {
+	ocs := p.ocsClient()
+	body, _ := json.Marshal(map[string]any{
+		"configKey":   p.Key,
+		"configValue": value,
+		"sensitive":   0,
+	})
+	_, err := ocs.Call(http.MethodPost, "apps/app_api/api/v1/ex-app/preference", body)
+	return err
+}
+
+func decodePreferenceValue(raw []byte, key string) (string, error) {
+	var parsed struct {
+		OCS struct {
+			Data []struct {
+				ConfigKey   string `json:"configkey"`
+				ConfigValue string `json:"configvalue"`
+			} `json:"data"`
+		} `json:"ocs"`
+	}
+	if err := json.Unmarshal(raw, &parsed); err != nil {
+		var items []struct {
+			ConfigKey   string `json:"configkey"`
+			ConfigValue string `json:"configvalue"`
+		}
+		if err2 := json.Unmarshal(raw, &items); err2 != nil {
+			return "", fmt.Errorf("preferences decode: %w", err)
+		}
+		for _, it := range items {
+			if it.ConfigKey == key {
+				return strings.TrimSpace(it.ConfigValue), nil
+			}
+		}
+		return "", nil
+	}
+	for _, it := range parsed.OCS.Data {
+		if it.ConfigKey == key {
+			return strings.TrimSpace(it.ConfigValue), nil
+		}
+	}
+	return "", nil
+}