Added finger functionality to WebFingerService

ref https://linear.app/tryghost/issue/MOM-120

We need to do this to lookup the inbox which we need to send a Follow activity

ghost/ghost/src/core/activitypub/webfinger.service.test.ts

@@ -0,0 +1,79 @@
+import assert from 'assert';
+import {ActorRepository} from './actor.repository';
+import {WebFingerService} from './webfinger.service';
+import {Actor} from './actor.entity';
+
+describe('WebFingerService', function () {
+    describe('getResource', function () {
+        it('Throws with invalid resource', async function () {
+            const repository: ActorRepository = {} as ActorRepository;
+            const service = new WebFingerService(repository, new URL('https://activitypub.server'));
+
+            await service.getResource('invalid').then(
+                () => {
+                    throw new Error('Should have thrown');
+                },
+                (err) => {
+                    assert.ok(err);
+                }
+            );
+        });
+
+        it('Throws with missing actor', async function () {
+            const repository: ActorRepository = {
+                async getOne() {
+                    return null;
+                }
+            } as unknown as ActorRepository;
+            const service = new WebFingerService(repository, new URL('https://activitypub.server'));
+
+            await service.getResource('invalid').then(
+                () => {
+                    throw new Error('Should have thrown');
+                },
+                (err) => {
+                    assert.ok(err);
+                }
+            );
+        });
+
+        it('Responds with webfinger for found actors', async function () {
+            const actor = Actor.create({username: 'c00ld00d'});
+            const repository: ActorRepository = {
+                async getOne() {
+                    return actor;
+                }
+            } as unknown as ActorRepository;
+            const url = new URL('https://activitypub.server');
+            const service = new WebFingerService(repository, url);
+
+            const subject = 'acct:c00ld00d@activitypub.server';
+            const result = await service.getResource(subject);
+
+            assert.deepEqual(result, {
+                subject,
+                links: [{
+                    rel: 'self',
+                    type: 'application/activity+json',
+                    href: actor.getJSONLD(url).id
+                }]
+            });
+        });
+    });
+
+    describe('#finger', function () {
+        it('Throws with invalid usernames', async function () {
+            const repository: ActorRepository = {} as ActorRepository;
+            const service = new WebFingerService(repository, new URL('https://activitypub.server'));
+
+            await service.finger('invalid').then(
+                () => {
+                    throw new Error('Should have thrown');
+                },
+                (err) => {
+                    assert.ok(err);
+                }
+            );
+        });
+    });
+});

ghost/ghost/src/core/activitypub/webfinger.service.ts

@@ -1,7 +1,8 @@
 import {Inject} from '@nestjs/common';
 import {ActorRepository} from './actor.repository';
 
-const accountResource = /acct:(\w+)@(\w+)/;
+const accountResourceMatcher = /acct:(\w+)@(\w+)/;
+const usernameMatcher = /@?(.+)@(.+)/;
 export class WebFingerService {
     constructor(
         @Inject('ActorRepository') private repository: ActorRepository,
@@ -10,7 +11,7 @@ export class WebFingerService {
 
     // eslint-disable-next-line @typescript-eslint/no-unused-vars
     async getResource(resource: string, rel?: string[]) {
-        const match = resource.match(accountResource);
+        const match = resource.match(accountResourceMatcher);
         if (!match) {
             throw new Error('Invalid Resource');
         }
@@ -36,4 +37,43 @@ export class WebFingerService {
 
         return result;
     }
+
+    async finger(handle: string) {
+        const match = handle.match(usernameMatcher);
+
+        if (!match) {
+            throw new Error('Invalid username');
+        }
+
+        const username = match[1];
+        const host = match[2];
+
+        let protocol = 'https';
+
+        // TODO Never in prod
+        if (host.startsWith('localhost') || host.startsWith('127.0.0.1')) {
+            protocol = 'http';
+        }
+
+        const res = await fetch(`${protocol}://${host}/.well-known/webfinger?resource=acct:${username}@${host}`);
+
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        const json: any = await res.json();
+
+        if (json.subject !== `acct:${username}@${host}`) {
+            throw new Error('Subject does not match - not jumping thru hoops');
+        }
+
+        const self = json.links.find((link: any) => link.rel === 'self');
+
+        const selfRes = await fetch(self.href, {
+            headers: {
+                accept: self.type
+            }
+        });
+
+        const data = await selfRes.json();
+
+        return data as any;
+    }
 }