Expose the function that gets fb data from an access token

[gsabran]

It's possible to get an access token directly, for instance with mobile application. To make it easier to handle those access tokens on the backend, I split the function that handles the token from the larger function that starts with the code.

This enables things like handling fb login directly from an access token:

let fbAppId = null;
export const loginWithFacebook = (params, req, res) => {
  const fbAccessToken = req.body.token;

  // make sure the access token is for our app
  const fbAppIdForToken = JSON.parse(HTTP.get(
    "https://graph.facebook.com/app", {
      params: { access_token: fbAccessToken }
    }).content).id;
  // get our app id
  if (!fbAppId) {
    const config = ServiceConfiguration.configurations.findOne({service: 'facebook'});
    fbAppId = config.appId;
  }
  if (fbAppId !== fbAppIdForToken) {
    // handle incorrect token
    return;
  }

  const expiresAt = req.body.expiresAt;
  const authResult = Facebook.handleAuthFromAccessToken(fbAccessToken, expiresAt);

  const { userId } = Accounts.updateOrCreateUserFromExternalService(
    'facebook',
    authResult.serviceData,
    authResult.options
  );
  ...
};

[apollo-cla]

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[gsabran]

@meteor-bot done :)

[tmeasday]

Thanks @gsabran, seems reasonable.

[tmeasday]

@gsabran are you interested in further maintaining the facebook packages? We are looking for maintainers for some of our more peripheral packages.

[gsabran]

I'm happy to contribute when it's easy for me! I'm still the only dev at my startup so I don't have much extra bandwidth. And I'd rather not take responsibilities I can't honor. That being said, I'm happy to contribute as much as I can. So I'd rather not tell you that I'd maintain the package, but I'll try to be helpful.

I'm working on integrating 3rd parties services from mobile clients with a Meteor backend. They (so far for Facebook at least) have flows that differ from web based oauth. I'll make PR when I think it makes sense to bring more flexibility in the accounts packages.

[VitalyChe]

@gsabran Thank you for your commit, I am just looking into authenticating FB/Google the same way as you proposed for mobile apps. What do you think about Google, could it be done the same way?
Thanks

[gsabran]

I haven't look into Google yet, but will probably soon. If that's helpful, here's the full code I'm been using things for Facebook mobile auth in my code: https://gist.github.com/gsabran/8bab053beb05a0a5bf871b4caa00f9b6

[VitalyChe]

@gsabran Thank you