feat: add DID document (#202)

Serve a DID document for the gateway at `/.well-known/did.json`.

Author: alanshaw

src/index.js

@@ -27,6 +27,7 @@ import {
   withDelegationStubs,
   withOptionsRequest,
   withCarParkFetch,
+  withDidDocumentHandler,
   withFormatRawHandler,
   withFormatCarHandler
 } from './middleware/index.js'
@@ -50,6 +51,7 @@ const middleware = composeMiddleware(
   withVersionHeader,
   withErrorHandler,
   withGatewayIdentity,
+  withDidDocumentHandler,
   withDelegationsStorage,
 
   // Handle UCAN invocations (POST requests only)

src/middleware/index.js

@@ -11,6 +11,7 @@ export { withEgressTracker } from './withEgressTracker.js'
 export { withFormatCarHandler } from './withFormatCarHandler.js'
 export { withFormatRawHandler } from './withFormatRawHandler.js'
 export { withDelegationStubs } from './withDelegationStubs.js'
+export { withDidDocumentHandler } from './withDidDocumentHandler.js'
 export { withGatewayIdentity } from './withGatewayIdentity.js'
 export { withUcanInvocationHandler } from './withUcanInvocationHandler.js'
 export { withDelegationsStorage } from './withDelegationsStorage.js'

src/middleware/withDidDocumentHandler.js

@@ -0,0 +1,40 @@
+/**
+ * @import { Middleware, Environment } from '@web3-storage/gateway-lib'
+ * @import { GatewayIdentityContext } from './withGatewayIdentity.types.js'
+ */
+
+/**
+ * Handles a GET request for `/.well-known/did.json` and passes on all other
+ * requests to the next handler in the chain.
+ *
+ * @type {Middleware<GatewayIdentityContext, GatewayIdentityContext, Environment>}
+ */
+export function withDidDocumentHandler (handler) {
+  return async (request, env, ctx) => {
+    if (request.method !== 'GET' || new URL(request.url).pathname !== '/.well-known/did.json') {
+      return handler(request, env, ctx)
+    }
+
+    const webKey = ctx.gatewayIdentity.did()
+    const publicKeyMultibase = ctx.gatewaySigner.did().replace('did:key:', '')
+    const verificationMethods = [
+      {
+        id: `${webKey}#owner`,
+        type: 'Ed25519VerificationKey2020',
+        controller: webKey,
+        publicKeyMultibase
+      }
+    ]
+
+    const headers = { 'Content-Type': 'application/json' }
+    const body = JSON.stringify({
+      '@context': ['https://w3id.org/did/v1'],
+      id: webKey,
+      verificationMethod: verificationMethods,
+      assertionMethod: verificationMethods.map(k => k.id),
+      authentication: verificationMethods.map(k => k.id)
+    }, null, 2)
+
+    return new Response(body, { headers })
+  }
+}

test/miniflare/freeway.spec.js

@@ -67,6 +67,8 @@ describe('freeway', () => {
         CONTENT_CLAIMS_SERVICE_URL: claimsService.url.toString(),
         CARPARK_PUBLIC_BUCKET_URL: url.toString(),
         GATEWAY_SERVICE_DID: 'did:example:gateway',
+        // did:key:z6MkvB4hvuVZhkKsi67rUKtNTKN4gpWjvWCoGPpBpGUdJMpF
+        GATEWAY_PRINCIPAL_KEY: 'MgCatBcQ1htL3Q/kXNZ9idtpoP9EeFxUSXD106hMWXc8si+0B6ZTgeQlqgoY9Z21skaKK6FpFRAAEF50T1c9WhWTa14w=',
         DAGPB_CONTENT_CACHE: 'DAGPB_CONTENT_CACHE',
         FF_DAGPB_CONTENT_CACHE_ENABLED: 'true',
         FF_DAGPB_CONTENT_CACHE_TTL_SECONDS: 300,
@@ -763,4 +765,29 @@ describe('freeway', () => {
     assertBlobEqual(input, await res.blob())
     assert.equal(cachedContent.keys.length, 0, 'Cache should be empty')
   })
+
+  it('should return DID document', async () => {
+    const res = await miniflare.dispatchFetch(
+      'http://localhost:8787/.well-known/did.json'
+    )
+    assert(res.ok)
+    const didDoc = await res.json()
+
+    assert(didDoc)
+    assert(typeof didDoc === 'object')
+
+    assert('id' in didDoc)
+    assert.equal(didDoc.id, 'did:example:gateway')
+
+    assert('verificationMethod' in didDoc)
+    assert(Array.isArray(didDoc.verificationMethod))
+    assert(didDoc.verificationMethod.length === 1)
+
+    const method = didDoc.verificationMethod[0]
+    assert('publicKeyMultibase' in method)
+    assert.equal(
+      method.publicKeyMultibase,
+      'z6MkvB4hvuVZhkKsi67rUKtNTKN4gpWjvWCoGPpBpGUdJMpF'
+    )
+  })
 })