Vue router optional first parameter

I have a list of routes that can all have an optional first parameter. If the parameter is present in the url, it will change a header I use in my api calls. Everything else remains the same.

Rather than create two sets of routes to handle this, is there a way I can list the first parameter as optional and only define my routes once?

For all routes, there can be an :environment param present in the front:

/:environment/:event_identifier/register/pages/:page_uuid

or it can be:

/:event_identifier/register/pages/:page_uuid

Everything else will remain the same.

let routes = [{
   path: '/:event_identifier/register/pages/:page_uuid',
   name: 'ContentPage',
   component: ContentPage,
   meta: {
      requiresAuth: true,
   },
}, {
   path: '/:event_identifier/register/:pagenum',
   name: 'Register',
   component: Register,
   meta: {
      requiresAuth: true,
   },
}, {
   path: '/:event_identifier',
   name: 'Login',
   component: Login,
   children: [{
      path: '/:event_identifier/:registration_uuid/:pagenum',
      name: 'editRegistration',
      component: Login,
   }]
}]