var oauth2orize = require('oauth2orize-koa');
var oauth2orizeFacebook = require('oauth2orize-koa-facebook');

var server = oauth2orize.createServer();

server.exchange(oauth2orizeFacebook.exchange.facebook(['email', 'first_name', 'last_name'], function (client, profile) {
  // Get access token from client and Facebook profile information.
  var accessToken = 'access token';

  // Refresh token could be returned if it is supported by your OAuth2 server.
  // If not available, just pass `null` as argument.
  var refreshToken = 'optional refresh token';

  // Additional parameters to return in response. Pass `null` if not available.
  var params = {
    'welcome_to': 'our OAuth2 server',
    'glad_to': 'meet you'
  };

  return [accessToken, refreshToken, params];
  // Or just `return accessToken` is enough.
}));