node.js example on how to connect to the grin-wallet owner API based on: it is a modified official example from here: https://github.com/mimblewimble/grin-wallet/tree/1ced8990b9e21fa17c788d93a151ec1164ebbce5/doc/samples/v3_api_node

index.js

/* Sample Code for connecting to the V3 Secure API via Node
 *
 * With thanks to xiaojay of Niffler Wallet:
 * https://github.com/grinfans/Niffler/blob/gw3/src/shared/walletv3.js
 *
 */

const http = require('http');
const crypto = require('crypto');

// Demo implementation of using `aes-256-gcm` with node.js's `crypto` lib.
const aes256gcm = (shared_secret) => {
	const ALGO = 'aes-256-gcm';

	// encrypt returns base64-encoded ciphertext
	const encrypt = (str, nonce) => {
		let key = Buffer.from(shared_secret, 'hex')
		const cipher = crypto.createCipheriv(ALGO, key, nonce)
		const enc = Buffer.concat([cipher.update(str, 'utf8'), cipher.final()])
		const tag = cipher.getAuthTag()
		return Buffer.concat([enc, tag]).toString('base64')
	};

	// decrypt decodes base64-encoded ciphertext into a utf8-encoded string
	const decrypt = (enc, nonce) => {
		//key,nonce is all buffer type; data is base64-encoded string
		let key = Buffer.from(shared_secret, 'hex')
		const data_ = Buffer.from(enc, 'base64')
		const decipher = crypto.createDecipheriv(ALGO, key, nonce)
		const len = data_.length
		const tag = data_.slice(len-16, len)
		const text = data_.slice(0, len-16)
		decipher.setAuthTag(tag)
		const dec = decipher.update(text, 'binary', 'utf8') + decipher.final('utf8');
		return dec
	};

	return {
		encrypt,
		decrypt,
	};
};

function requestAsync(payload_json, auth) {
	return new Promise((resolve, reject) => {
		const payload = JSON.stringify(payload_json)
		const options = {
			'host': 'localhost',
			'port': 3420,
			'path': '/v3/owner',
			'auth': auth,
			'headers': {
				'Content-Type': 'application/json',
				'Content-Length': payload.length
			},
			'method': 'POST'
		}	
		const req = http.request(options, (response) => {
			let data = ''
			response.on('data', (chunk) => {
				data += chunk
			})
			response.on('end', () => {
				// console.log(response.statusCode)
				resolve(JSON.parse(data))
			})
			response.on('error', (err) => {
				reject(err)
			})
		})
		req.write(payload)
		req.end()
	})
}

async function encryptedPayload(rpc_data, aesCipher) {
	const nonce = new Buffer.from(crypto.randomBytes(12));
	const enc = aesCipher.encrypt(JSON.stringify(rpc_data), nonce);
	return {
		'nonce': nonce.toString('hex'),
		'body_enc': enc,
	}
}

async function main() {
	let ecdh = crypto.createECDH('secp256k1')
	ecdh.generateKeys()
	let publicKey = ecdh.getPublicKey('hex', 'compressed')

	console.log('\nour public key')
	console.log(publicKey)

	const auth = 'grin:secret_api_key'

	payload = {
		'jsonrpc': '2.0',
		'method': 'init_secure_api',
		'params': {
			'ecdh_pubkey': publicKey
		},
		'id': 1
	}

	const response = await requestAsync(payload, auth)
	// console.log(response)
	console.log('\nserver public key')
	console.log(response.result.Ok)
	
	const shared_secret = ecdh.computeSecret(response.result.Ok, 'hex', 'hex')
	console.log('\nshared secret')
	console.log(shared_secret)

	const rpc_data = {
		'jsonrpc': '2.0',
		'method': 'accounts',
		'params': {
			'token': '12345',
		},
		'id': 1
	}

	const aesCipher = aes256gcm(shared_secret);
	const params = await encryptedPayload(rpc_data, aesCipher)

	const payload_json2 = {
		'jsonrpc': '2.0',
		'method': 'encrypted_request_v3',
		'params': params,
		'id': 1
	}
	// console.log(payload_json2)
	const response2 = await requestAsync(payload_json2, auth)

	// console.log(response2)
	const nonce2 = Buffer.from(response2.result.Ok.nonce, 'hex');
	const data = Buffer.from(response2.result.Ok.body_enc, 'base64');

	const dec = aesCipher.decrypt(data, nonce2)
	const dec_parsed = JSON.parse(dec)
	console.log('\ndecrypted response from the wallet')
	console.log(dec_parsed)
}

main()

package.json

{
  "name": "node-sample",
  "version": "0.0.1",
  "description": "Sample of connecting to the secure OwnerAPI via node",
  "main": "src/index.js",
  "scripts": {
    "test": "npm test"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
  }
}