app.yaml

application: GAE_APP_IDENTIFIER
version: 1
runtime: python27
api_version: 1
threadsafe: yes

handlers:
- url: .*
  script: main.app

libraries:
- name: webapp2
  version: 2.5.2
- name: webob
  version: 1.2.3

inbound_services:
- warmup

main.py

import json
import uuid

from google.appengine.ext import ndb

import webapp2
from webapp2_extras.routes import RedirectRoute


def _parse_request(request):
    if request.content_type == 'application/json':
        try:
            body_json = json.loads(request.body)
            provider_name = body_json.get('provider_name', None)
            provider_user_id = body_json.get('provider_user_id', None)
        except ValueError:
            return webapp2.abort(400, detail='invalid json')
    else:
        provider_name = request.params.get('provider_name', None)
        provider_user_id = request.params.get('provider_user_id', None)

    return provider_name, provider_user_id


class Provider(ndb.Model):
    name = ndb.StringProperty(required=True)


class Identity(ndb.Model):
    user = ndb.KeyProperty(kind='GlobalUser')


class GlobalUser(ndb.Model):
    uuid = ndb.StringProperty(required=True)

    @property
    def identities(self):
        return Identity.query(Identity.user==self.key).fetch()


class ResolveHandler(webapp2.RequestHandler):
    @ndb.toplevel
    def post(self):
        provider_name, provider_user_id = _parse_request(self.request)

        if not provider_name or not provider_user_id:
            return self.abort(400, detail='missing provider_name and/or provider_user_id')

        identity = ndb.Key(Provider, provider_name, Identity, provider_user_id).get()

        if identity:
            user_uuid = identity.user.id()
        else:
            user_uuid = uuid.uuid4().hex

            GlobalUser(
                id=user_uuid,
                uuid=user_uuid
            ).put_async()

            Identity(
                parent=ndb.Key(Provider, provider_name),
                id=provider_user_id,
                user=ndb.Key(GlobalUser, user_uuid)
            ).put_async()

        return webapp2.Response(
            status='200 OK',
            content_type='application/json',
            body = json.dumps({
                'provider_name' : provider_name,
                'provider_user_id' : provider_user_id,
                'uuid' : user_uuid
            })
        )

app = webapp2.WSGIApplication([
      RedirectRoute('/v1/resolve', ResolveHandler, 'resolve', strict_slash=True)
], debug=False)