Data Union Join Server

This is a gatekeeper HTTP server for requiring Data Union members to fulfil certain requirements in order to join a Data Union. Example use cases are limiting members to users of a certain application by requiring an application secret to be passed along with the join request, or preventing bots by requiring users to complete a CAPTCHA.

The process of joining a Data Union is generally as follows:

• At Data Union creation time, a joinPartAgent Ethereum address is configured on the Data Union smart contract. The joinPartAgent is able to add members to the Data Union.
• This Data Union join server is configured with the private key for the joinPartAgent address.
• When a member wants to join via the Data Union application, a HTTP request is sent to this join server.
• The join server validates the join request (by validating app secret, captcha, or whatever is needed), and then makes a blockchain transaction to add the member to the Data Union.

Data Union builder teams can easily extend the validation logic and run their own join server. Implementing any kind of join request validation logic is possible.

As an alternative to running your own customized join server, the Data Union DAO hosts a default join server, which also extends this base package and implements a validation logic based on application secrets stored in a database. Forking that as a starting point may be an easier way to get started on your own customizations, or you can follow the instructions in this readme to start the customizations from scratch.

This package can also be run as-is, in which case the join server performs only signature validation and therefore allows anyone to join a Data Union.

Usage

The most typical use case for this package is to extend the functionality of the join server by adding custom validation logic and/or additional HTTP endpoints.

• Start a new node.js project for your custom join server
• Install this base package as a dependency:

npm install --save @dataunions/join-server

• Then you can use the server in your application:

const { JoinServer } = require('@dataunions/JoinServer')

const srv = new JoinServer({
    // Always pass in the private key for the wallet you set as the joinPartAgent
    privateKey: '...',

    // Additional options, see below
    ...
})
srv.listen()

That's exactly what's happening in the default join server. Forking that may be a faster starting point for your own customizations, or you can study this readme to start your customizations from scratch.

Note that this base join server does not grant the joining member permissions to any data backend, it just adds the member to the smart contract. In your join server, you should grant the joining member the ability to share their data via whatever data backend/protocol your Data Union is using via using the onMemberJoin hook (see Options).

The default join server hosted by the Data Union DAO is Streamr-aware, meaning that it grants new members publish permission to Streamr streams associated with that Data Union. If you're using a different data protocol/backend, you need to grant access to your data backend to your new DU members (unless of course your backend accepts data from anyone, not just DU members).

Options

See below for the various constructor options and their default values. At a minimum, you should pass in at least the privateKey.

new JoinServer({
    // Hex-encoded private key for your joinPartAgent address
    privateKey: '...', 

    // HTTP port the server listens on
    port: 5555,

    // Logger (pino) level: one of 'fatal', 'error', 'warn', 'info', 'debug', 'trace' or 'silent'.
    logLevel: 'info',

    // Used to validate custom fields in join requests. The default function does nothing.
    customJoinRequestValidator: async (address, joinRequest) => {},

    // Used to add custom routes to the HTTP server. The default function does nothing.
    customRoutes: (expressApp) => {},

	// Gets called after a member is successfully joined to the Data Union smart contract. The default function does nothing.
	onMemberJoin = async (/* member, dataUnion, chain */) => {},

    // By default public RPCs are used for each chain, but you can pass this option to override
    customRPCs: {
        polygon: 'https://my-custom-polygon-rpc-address',
        gnosis: 'https://my-custom-gnosis-rpc-address',
    }
})

Running as-is

You can also run the "base" join server without any customizations. This may be useful for development and testing. Note that the base join server only does the signature validation, meaning that anyone (including bots etc.) can join your data unions.

npm install -g @dataunions/join-server
join-server -k <private key>

For other command-line options, see the help available at join-server -h.

Extending

The functionality of the join server can be extended by data union teams in two important ways: validating custom fields in join requests, and adding custom HTTP endpoints.

Adding custom fields to join requests

In many cases, you'll want to pass some additional information from the end-user app to the join server, such as CAPTCHA responses or other information used to accept the new member. In that case, the join request will have the dataUnion and chain keys plus your custom ones for which you can choose any names you want:

{
    "dataUnion": "0x12345",
    "chain": "polygon",
    "myCustomSecret": "foo"
}

To inject your custom validation logic to the join server, pass the customJoinRequestValidator function to the constructor. This is an async function (returns a promise) that is expected to resolve if the validation passes, or reject if it fails. For example:

const srv = new JoinServer({
    ...
    customJoinRequestValidator = async (joinRequest) => {
        if (joinRequest.myCustomSecret !== 'foo') {
            throw new Error('My custom secret is incorrect!')
        }
    },
})

Adding custom endpoints

Custom endpoints (routes) can be created on the server by passing in a customRoutes function, which receives the express app instance as an argument.

All requests pass through the signature validation middleware, which makes the parsed and validated content of the request payload available as req.validatedRequest.

Here's a simple example of a custom endpoint POST /hello that reads payloads with a message field in them:

const srv = new JoinServer({
    ...
    customRoutes = (expressApp) => {
        expressApp.post('/hello', function(req, res, next) {
            res.status(200)
            res.set('content-type', 'application/json')
            res.send({
                // Fields in the request payload can be accessed via req.validatedRequest
                message: req.validatedRequest.message,
                // Fields in the raw request (signed wrapper) can be accessed via req.body
                from: req.body.address,
            })
        })
    },
})

In the context of the signed message wrapper, the full request to this endpoint would look like this (see Authentication):

{
   "address": "...",
   "request": "{\"message\":\"Hi there!\"}",
   "timestamp": "...",
   "signature": "..."
}

Authentication

All endpoints exposed by the join server expect requests to be signed with the requesting Ethereum wallet using a simple signature scheme. The details are below, however most users shouldn't need to implement the authentication from scratch, but instead simply use the Data Union client.

Requests to the join server look like this:

{
   "address": "0xf79d101E1243cbDdE02d0F49E776fA65de0122ed",
   "request": "{\"foo\":\"bar\"}",
   "timestamp": "2022-07-01T00:00:00.000Z",
   "signature": "0xefde1ff335c8fb28fe9f49c87c39c21659b5ad1a6967d154c4d4ea1978f572a02c7d82f8ab5828b7550246220919594bc84361cb50a89ce74a957eefc59dd4a41b"
}

• request - the actual request as stringified JSON
• address - the Ethereum address that originated the request
• timestamp - timestamp of the request in ISO 8601 format. The join server will by default reject requests with timestamps more than 5 minutes off from current time
• signature - a hex-encoded signature produced by signing the request with the private key of address using the Ethereum message signing (for example signer.signMessage() in ethers)

Different endpoints expect different types of content in request. Users that extend the server can add new endpoints and submit arbitrary request content.

HTTP Endpoints

This base package only exposes one endpoint, which is used for submitting join requests.

/join

Expects the request in the wrapper object to be of form:

{
    "dataUnion": "0x12345",
    "chain": "polygon"
}

or in other words, the full signed HTTP request body would be:

{
   "address": "0xabcdef",
   "request": "{\"dataUnion\":\"0x12345\",\"chain\":\"polygon\",}",
   "timestamp": "...",
   "signature": "..."
}

Such a request would join address (0xabcdef) as member of the Data Union at smart contract address 0x12345, to be found on the Polygon chain.

The join request can contain arbitrary additional fields, which are validated by passing to the server a customJoinRequestValidator function - see below for information about extending and customizing the server.

The response sent by the server has the form:

{
    "member": "0xabcdef",
    "dataUnion": "0x12345",
	"chain": "polygon"
}

Developing

To learn about building and developing this software, see developing.md.