How to set realm id and partition with custom login?

MongoDB Realm Realm Sync
#1

Hello,

I’m using a custom authentication function so that a mobile client generates a unique id and logs in with it.

My function is

exports = async function(loginPayload) {
  const app_secret = "somesecret"
  
  const users = context.services
    .get("mongodb-atlas")
    .db("app")
    .collection("UserInfo");

  const { clientUserId, secret } = loginPayload;
  
  if(app_secret !== secret) {
    throw "Secret mismatch : " + secret;
  }

  const user = await users.findOne({ clientUserId: clientUserId });
  
  if (user) {
    return user._id.toString();
  } else {
    const newId = new BSON.ObjectId();
    const partition = "user=" + newId.toString();
    const result = await users.insertOne({ _id: newId, _partition: partition, clientUserId: clientUserId, creationDate: new Date() });
    return result.insertedId.toString();
  }
};

My problem is that the “realm user id”, the one that RealmSDK gives me on mobile client is different from the one I generate in the custom function.

And I have set the permissions to

READ 
(can only read PUBLIC and your own data such as partitions are "user=myId123" or "PUBLIC")
{
  "$or": [
    {
      "%%partition": "user=%%user.id"
    },
    {
      "%%partition": "PUBLIC"
    }
  ]
}

WRITE 
(can only write your own data such as partitions are "user=myId123")
{
  "%%partition": "user=%%user.id"
}

How am I supposed to retrieve this realm user id so that I can set up correctly my custom login function and populate correctly my collection with the right _partition and _id?

EDIT: The error I get from Realm Sync Backend is

Error: user does not have permission to sync on partition (ProtocolErrorCode=206)
Partition: user=607ac1b7687c4dca433c3c5e

Because my custom function has set the custom user id to 607ac1b7687c4dca433c3c5b but the actual realm user id is 607ac1b7687c4dca433c3c5e and I have no clue how to fetch this id from the custom login function…

#3

Could You solve the problem? I have the same problem…

#4

Hi Marco,

Yes I found a solution. However, it’s not a straightforward solution, I have to do it in 2 steps:

Schema
I have a collection called UserInfo which I use for saving users.

UserInfo
  _id: ObjectId
  _partition: String
  creationDate: Date
  gameCenterId: Optional String
  appleId: Optional String
  {any_other_login_method_id: Optional String}

Step 1.
I set up my “Custom Function Authentication” - by the way I use GameCenter (an iOS game framework which gives me a unique user id).

Here is the code.

exports = async function(loginPayload) {
  const users = context.services
    .get("mongodb-atlas")
    .db("app")
    .collection("UserInfo");
  
  let findQuery;
  if (loginPayload["gameCenterId"] != null) {
    findQuery = { gameCenterId: loginPayload["gameCenterId"] };
  }

  // Check if user already exists using our own GameCenter_id
  const user = await users.findOne(findQuery);
  
  if (user !== null) {
    return user._id.toString();
  } else {
    // Set the partition to a temporary value.
    // A onCreate trigger will replace it with user={InternalRealmId} which we still don't have here because of custom-function internal logic
    const temporaryId = new BSON.ObjectId();
    if (loginPayload["gameCenterId"] != null) {
      const result = await users.insertOne({
        _id: temporaryId,
        _partition: "temporaryId=" + temporaryId.toString(),
        creationDate: new Date(),
        gameCenterId: loginPayload["gameCenterId"]
      });
      return result.insertedId.toString();
    }
  }
};

Step 2.
Then I create a trigger that will always run for every created user with the custom function login. This trigger’s goal is to inject and override the realm_id into the partition of the previous document created.

Here is its configuration:

  • Trigger type: Authentication
  • Enabled: True
  • Action type: Create
  • Provider: Custom Function Authentication
  • Select an event type: Function
  • Function: {my function called onUserCreated}

And here is my onUserCreated function

exports = async function(authEvent) {
  const user = authEvent.user;
  const realmUserId = user.id; // Now we have the actual realm_id
  const identities = user.identities;
  
  // Update our user's Mongo document's partition with the actual realm_id
  const customIdentity = identities.find(identity => identity.provider_type === "custom-function");
  if (customIdentity !== undefined) {
    const userId = new BSON.ObjectId(customIdentity.id);
    const collection = context.services.get("mongodb-atlas").db("app").collection("UserInfo");
    const findUser = await collection.findOne({ _id: userId });
    if (findUser !== null) {
      await collection.updateOne({ "_id": userId }, { $set: { 
        _partition: "user=" + realmUserId.toString()
      } });
      return;
    } else {
      return;
    }
  }
};

And voila… I only had a few problems (maybe once per month or so) with the shared cluster and according to Realm support, shared clusters can have very rare trigger failures apparently.

#5

Hi Jerome,

You are my hero; thank you so much!

You saved my day!!

#6

You are welcome :slight_smile:

(Would be nice if Realm could add a tutorial to their documentation - so that we would finally know the official way.)