Use resolvable ActivityPub keyId

src/remote/activitypub/request.ts

@@ -35,7 +35,7 @@ export default (user: ILocalUser, url: string, object: any) => new Promise((reso
 	sign(req, {
 		authorizationHeaderName: 'Signature',
 		key: user.keypair,
-		keyId: `acct:${user.username}@${config.host}`
+		keyId: `${config.url}/users/${user._id}/publickey`
 	});
 
 	// Signature: Signature ... => Signature: ...