Example async setting headers in adapter.

overriden-adapter.js

import DS from 'ember-data';

export default DS.RESTAdapter.extend({
    async ajax(...args) {
        // Store the parent call, so it can be called after getting the current session.
        const _super = this._super.bind(this);

        // Sorry, I'm unfamiliar with how you're accessing amplify
        const headers = await amplify.currentSession();

        this.set('headers', {
            'Authentication': headers.auth
        });

        return _super(...args);
    }
});