Meteor slingshot file upload to Google Cloud Storage internal server error

I am trying to upload files using edgee:slingshot, but I have several errors. I have did everything as described in github page. This is my settings on server:

Slingshot.GoogleCloud.directiveDefault.GoogleSecretKey = Assets.getText('google-cloud-service-key.pem');

Slingshot.createDirective("myFileUploads", Slingshot.GoogleCloud, {
    bucket: 'dossum-app',
    GoogleAccessId: "GOOGXXXX",
    GoogleSecretKey: "qZEsLZ/NiXXXXXXXXXXXXUW8NVjSvRb8SgdxXXXXX2",
    acl: 'bucket-owner-full-control',
    authorize: function() {
        if (!this.userId) {
            var message = 'Please login before posting file';
            throw new Meteor.Error('Login Required', message);
        }

        return true;
    },
    key: function(file) {
        var user = Meteor.users.findOne(this.userId);
        return user.username + '/' + file.name;
    }
});

And this is cors.json:

[{"origin": ["http://localhost:3000", "http://qnekt.zehinz.com"], "responseHeader": ["Origin", "Accept", "X-Requested-With", "Authorization", "Content-Type", "Content-Length", "Accept-Encoding", "X-CSRF-Token"], "method": ["GET", "HEAD", "DELETE", "PUT", "POST", "HEAD"], "maxAgeSeconds": 3600}]

If I run with above configuration I get this error without any details: {error: 500, reason: "Internal server error".... I have tried to comment this line: //GoogleSecretKey:"qZEsLZ/NiEkXo641XHIUW8NVjSvRb8SgdxIyYcV2" This time I receive this error:

{error: "Forbidden - 403", reason: "Failed to upload file to cloud storage", details: undefined ...

Can anyone please guide me?

1. Where should I get GoogleAccessId if I am using .pem file instead of GoogleSecretKey?

2. What should be the cors.json file for file uploading and public reading?

I had troubles with edgee:slingshot and Google Cloud Storage. But this settings now work for me:

//server
Slingshot.GoogleCloud.directiveDefault.GoogleSecretKey = Assets.getText('google-cloud-service-key.pem');

Slingshot.createDirective('avatarUploader', Slingshot.GoogleCloud, {
    bucket: 'my_bucket',
    GoogleAccessId: 'xxxxxxxxxxxxxx@developer.gserviceaccount.com',
    acl: 'public-read',
    authorize: function() {
        if (!this.userId) {
            var message = 'Please login before posting file';
            throw new Meteor.Error('Login Required', message);
        }

        return true;
    },
    key: function(file) {
        var user = Meteor.users.findOne(this.userId);
        var ext = file.type.split('/')[1];
        return user.username + '/' + randomString(20) + '.' + ext;
    }
});

//CORS settings
[
  {
    "origin": ["*"],
    "responseHeader": ["*"],
    "method": ["GET", "POST", "PUT", "HEAD"],
    "maxAgeSeconds": 3000
  }
]

For details look here.