Consider async functions!

[RSNara]

Before

export default Torii.extend({
  torii: service('torii'),
  authenticate() {
    return new RSVP.Promise((resolve, reject) => {
      this._super(...arguments).then((data) => {
        raw({
          url:      `${config.apiHost}/api/tokens/oauth/grant`,
          type:     'POST',
          dataType: 'json',
          data:     { 'grant_type': 'facebook_auth_code', 'auth_code': data.authorizationCode }
        }).then((response) => {
          resolve({
            access_token: response.accessToken,
            provider: data.provider,
            user_id: response.userId
          })
        }, reject)
      }, reject)
    })
  }
})

After

export default Torii.extend({
  torii: service('torii'),
  async authenticate() {
    const data = await this._super(...arguments)
    const response = await raw({
      url:      `${config.apiHost}/api/tokens/oauth/grant`,
      type:     'POST',
      dataType: 'json',
      data:     { 'grant_type': 'facebook_auth_code', 'auth_code': data.authorizationCode }
    })
    return {
      access_token: response.accessToken,
      provider: data.provider,
      user_id: response.userId
    }
  }
})

Just thought it could simplify life (if you have the regenerator runtime installed).

[RSNara]

(Should probably try to move away from arguments too, but that's another discussion :P).