feat: ACL labels from environment variables (#422)

* feat: add LabelService to retrieve application labels from environment variables

* feat: allow usage of labels from docker and env variables simultaneously

Prioritize labels from environment variables over labels from docker
labels

* fix: handle error returned by label_serive.go/LoadLabels

see https://github.com/steveiliop56/tinyauth/pull/422#discussion_r2443443032

* refactor(label_service): use simple loop instead of slices.ContainsFunc to avoid experimental slices package
see https://github.com/steveiliop56/tinyauth/pull/422#pullrequestreview-3354632045

* refactor: merge acl logic into one service

---------

Co-authored-by: Stavros <steveiliop56@gmail.com>

internal/service/access_controls_service.go

@@ -0,0 +1,103 @@
+package service
+
+import (
+	"os"
+	"strings"
+	"tinyauth/internal/config"
+	"tinyauth/internal/utils/decoders"
+
+	"github.com/rs/zerolog/log"
+)
+
+type AccessControlsService struct {
+	docker  *DockerService
+	envACLs config.Apps
+}
+
+func NewAccessControlsService(docker *DockerService) *AccessControlsService {
+	return &AccessControlsService{
+		docker: docker,
+	}
+}
+
+func (acls *AccessControlsService) Init() error {
+	acls.envACLs = config.Apps{}
+	env := os.Environ()
+	appEnvVars := []string{}
+
+	for _, e := range env {
+		if strings.HasPrefix(e, "TINYAUTH_APPS_") {
+			appEnvVars = append(appEnvVars, e)
+		}
+	}
+
+	err := acls.loadEnvACLs(appEnvVars)
+
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (acls *AccessControlsService) loadEnvACLs(appEnvVars []string) error {
+	if len(appEnvVars) == 0 {
+		return nil
+	}
+
+	envAcls := map[string]string{}
+
+	for _, e := range appEnvVars {
+		parts := strings.SplitN(e, "=", 2)
+		if len(parts) != 2 {
+			continue
+		}
+
+		// Normalize key, this should use the same normalization logic as in utils/decoders/decoders.go
+		key := parts[0]
+		key = strings.ToLower(key)
+		key = strings.ReplaceAll(key, "_", ".")
+		value := parts[1]
+		envAcls[key] = value
+	}
+
+	apps, err := decoders.DecodeLabels(envAcls)
+
+	if err != nil {
+		return err
+	}
+
+	acls.envACLs = apps
+	return nil
+}
+
+func (acls *AccessControlsService) lookupEnvACLs(appDomain string) *config.App {
+	if len(acls.envACLs.Apps) == 0 {
+		return nil
+	}
+
+	for appName, appACLs := range acls.envACLs.Apps {
+		if appACLs.Config.Domain == appDomain {
+			return &appACLs
+		}
+
+		if strings.SplitN(appDomain, ".", 2)[0] == appName {
+			return &appACLs
+		}
+	}
+
+	return nil
+}
+
+func (acls *AccessControlsService) GetAccessControls(appDomain string) (config.App, error) {
+	// First check environment variables
+	envACLs := acls.lookupEnvACLs(appDomain)
+
+	if envACLs != nil {
+		log.Debug().Str("domain", appDomain).Msg("Found matching access controls in environment variables")
+		return *envACLs, nil
+	}
+
+	// Fallback to Docker labels
+	return acls.docker.GetLabels(appDomain)
+}