This fails linting due to the redeclaration of 'token', its also a bit of duplication we dont really need, I would suggest

    if (opts.auth || host.auth) { 
      var nAuth = opts.auth || host.auth;
      var token = PouchUtils.btoa(nAuth.username + ':' + nAuth.password);
      host.headers.Authorization = 'Basic ' + token; 
    }

Sound good?