feat(panel): add domain-admin role with per-domain authorization

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

internal/web/auth/principal.go

@@ -0,0 +1,86 @@
+package auth
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/mixeme/selfpost/internal/store"
+)
+
+type ctxKey int
+
+const (
+	usernameKey   ctxKey = 0
+	principalKey  ctxKey = 1
+)
+
+// Role is a panel user's access level.
+type Role = store.Role
+
+const (
+	RoleGlobal      = store.RoleGlobal
+	RoleDomainAdmin = store.RoleDomainAdmin
+)
+
+// Principal is the authenticated panel user attached to a request.
+type Principal struct {
+	ID       int64
+	Username string
+	Role     Role
+	Domains  []int64 // assigned domain IDs; empty for global (all domains)
+}
+
+// IsGlobal reports whether the principal has full panel access.
+func (p Principal) IsGlobal() bool {
+	return p.Role == RoleGlobal
+}
+
+// CanAccessDomain reports whether the principal may access a domain id.
+func (p Principal) CanAccessDomain(domainID int64) bool {
+	if p.IsGlobal() {
+		return true
+	}
+	for _, id := range p.Domains {
+		if id == domainID {
+			return true
+		}
+	}
+	return false
+}
+
+// CanAccessApp reports whether the principal may access an application.
+func (p Principal) CanAccessApp(app store.Application) bool {
+	return p.CanAccessDomain(app.DomainID)
+}
+
+func principalFromUser(u store.User) Principal {
+	return Principal{
+		ID:       u.ID,
+		Username: u.Username,
+		Role:     u.Role,
+		Domains:  u.DomainIDs,
+	}
+}
+
+func withPrincipal(ctx context.Context, p Principal) context.Context {
+	ctx = context.WithValue(ctx, usernameKey, p.Username)
+	return context.WithValue(ctx, principalKey, p)
+}
+
+// CurrentPrincipal returns the authenticated principal from the request context.
+func CurrentPrincipal(ctx context.Context) (Principal, bool) {
+	if v, ok := ctx.Value(principalKey).(Principal); ok {
+		return v, true
+	}
+	return Principal{}, false
+}
+
+// PrincipalFromRequest returns the authenticated principal from an HTTP request.
+func PrincipalFromRequest(r *http.Request) (Principal, bool) {
+	return CurrentPrincipal(r.Context())
+}
+
+// RequestWithPrincipal attaches a principal for middleware-equivalent tests.
+func RequestWithPrincipal(r *http.Request, p Principal) *http.Request {
+	return r.WithContext(withPrincipal(r.Context(), p))
+}