feat: add tenant authorization middleware

backend/internal/membership/context.go

@@ -0,0 +1,28 @@
+package membership
+
+import (
+	"context"
+	"net/http"
+
+	"proxui/backend/internal/rbac"
+)
+
+type Membership struct {
+	TenantID string    `json:"tenant_id"`
+	Role     rbac.Role `json:"role"`
+}
+
+type contextKey struct{}
+
+func ContextWithMembership(ctx context.Context, membership Membership) context.Context {
+	return context.WithValue(ctx, contextKey{}, membership)
+}
+
+func FromContext(ctx context.Context) (Membership, bool) {
+	membership, ok := ctx.Value(contextKey{}).(Membership)
+	return membership, ok
+}
+
+func FromRequest(r *http.Request) (Membership, bool) {
+	return FromContext(r.Context())
+}