docs(didcomm): first draft of didcomm setup for backend

docs/node_tutorials/node_didcomm.md

@@ -0,0 +1,147 @@
+---
+id: node_didcomm
+title: Communication between agents
+sidebar_label: Communication between agents
+---
+
+This guide covers setting up an app that emulates two agents communicating
+using [DIDCommMessaging](https://identity.foundation/didcomm-messaging/spec/)
+You will set up 2 agents. One that can listen to DIDComm messages and one that can send them.
+
+### Prerequisites
+
+Starting with the code from the [node setup tutorial](./node_setup_identifiers.md)
+
+Install some necessary Veramo plugins & `express`
+
+```bash
+yarn add express @veramo/message-handler @veramo/remote-server @veramo/did-jwt @veramo/did-comm @veramo/credential-w3c @veramo/data-store
+```
+
+## Extend your agent with the new plugins
+
+In your `./src/veramo/setup.ts`, add the following imports:
+
+```typescript
+import { MessageHandler } from '@veramo/message-handler'
+import { DIDComm, DIDCommMessageHandler } from '@veramo/did-comm'
+import { DataStore } from '@veramo/data-store'
+import { JwtMessageHandler } from '@veramo/did-jwt'
+import { CredentialIssuer, W3cMessageHandler } from '@veramo/credential-w3c'
+```
+
+add then add the following plugins to the array of `plugins` on the agent:
+
+```typescript
+plugins: [
+  //...
+  new CredentialIssuer(),
+  new DIDComm(),
+  new DataStore(dbConnection),
+  new MessageHandler({
+    messageHandlers: [
+      // in the case of message handlers, the order of handlers is important
+      new DIDCommMessageHandler(),
+      new JwtMessageHandler(),
+      new W3cMessageHandler(),
+    ],
+  }),
+]
+```
+
+## Create a listening agent
+
+We will set up a simple expressjs app that listens to incoming HTTP POST messages and sends them to Veramo. Create a
+file named `src/alice-agent.ts` and fill it with something like this:
+
+```typescript
+import { MessagingRouter, RequestWithAgentRouter } from '@veramo/remote-server'
+import { agent } from './veramo/setup'
+import express from 'express'
+
+const port = process.env.PORT || 3002
+
+const messagingRouter = MessagingRouter({
+  metaData: { type: 'express' },
+})
+
+const app = express()
+app
+  .use(RequestWithAgentRouter({ agent }))
+  .use(messagingRouter)
+  .listen(port, async () => {
+    console.log(`Local agent Alice listening for messages at ${port}`)
+  })
+```
+
+### Add a command for Alice
+
+To run this agent that can listen to messages add a new script to `package.json`:
+
+```ts
+  "scripts": {
+    // ...
+    "alice:listen": "ts-node ./src/alice-agent"
+  }
+```
+
+### test your setup
+
+You can now start your agent using `yarn alice:listen`.
+
+You can try to send Alice a credential to test your setup. In another terminal run the following:
+
+```bash
+curl -X POST -H "Content-Type: application/json"\
+ -d eyJhbGciOiJFUzI1NksiLCJ0eXAiOiJKV1QifQ.eyJ2YyI6eyJAY29udGV4dCI6WyJodHRwczovL3d3dy53My5vcmcvMjAxOC9jcmVkZW50aWFscy92MSJdLCJ0eXBlIjpbIlZlcmlmaWFibGVDcmVkZW50aWFsIiwiRXhhbXBsZSJdLCJjcmVkZW50aWFsU3ViamVjdCI6eyJoZWxsbyI6IndvcmxkIn19LCJzdWIiOiJodHRwczovL2V4YW1wbGUuY29tIiwibmJmIjoxNjM2Mzg0NTEyLCJpc3MiOiJkaWQ6ZXRocjpyaW5rZWJ5OjB4MDM0ODg4YTdiODhjMmJhZWMyMzkyM2E1OTk4ZTFjN2UwMTc5OTQwMGZjZjM0MjI0MzEzNDA2MDMwY2EzMzkyOTIwIn0.qWpFDpfl6Ml3CLiKIpS0hW3wJ4oW5b2mNXcVikuPhfLfwtzzHmI4tjFYxVXyrBYO_PtmY9B0D4P-f89wmgCsPQ\
+ http://localhost:3002
+```
+
+You should see something like this as a response:
+
+```json
+{
+  "id": "bf89b3f819896d4ba7b3d7af65da3046284a815778f7bdfb550a9748c908aad060f03f01f64d5d41b1a4d381c5c3f792c584fc852dc8a91c8d4fdc9b8ac84bee"
+}
+```
+
+### Some clarification:
+
+Once started, the agent is now listening to messages coming into port 3002. All http POST requests to that port will be
+interpreted as messages by the `MessageHandler` plugin.
+
+The flow of data is as follows:
+
+- With that `curl` command, a blob of data is sent to that endpoint.
+- `MessagingRouter` sends this data to the `handleMessage()` method that is provided by the `MessageHandler` plugin.
+- The first message handler tries to interpret the data, in our case `DIDCommMessageHandler`.
+- It is not a DIDComm message, so the blob of data is just forwarded to the next handler, `JwtMessageHandler`
+- This recognises it as a valid JWT and goes on to verify it.
+- Once verification passes, the next handler `W3CMessageHandler` is called using some extra metadata.
+- This last handler observes that the message is a valid W3C VerifiableCredential, so it saves it to the `DataStore`
+
+> With the current setup, the agent will store any data that looks valid. Later we will explore how to filter messages.
+
+## Adding DIDComm to the mix
+
+// TBD
+
+### didManagerAddService
+
+// TBD
+
+### spin up another agent
+
+// TBD
+
+### packDIDCommMessage
+
+// TBD
+
+### sendDIDCommMessage
+
+// TBD
+
+Congrats, You have set up two agents and sent a message from Bob to Alice.
+
+## Notes