Add a layer of safety around required ActivityPub Actor fields (#4703)

* fix(ap): add safe constructors, getters, and validators to ActivityPub actors to address #4701

* chore: replace nil check with the new Validate() method

* chore(test): added test to verify the values extracted from actors

* fix: return the specific error type + test for it

* fix(ap): add recovery for each AP inbox worker for a worst case scenario

* fix(ap): add additional safe accessor methods to other AP entities other than actors

* chore(tests): add tests for the new safe accessors

* fix(ap): handle empty public keys in AP actors

activitypub/inbox/update.go

@@ -4,6 +4,7 @@ import (
 	"context"
 
 	"github.com/go-fed/activity/streams/vocab"
+	"github.com/owncast/owncast/activitypub/apmodels"
 	"github.com/owncast/owncast/activitypub/persistence"
 	"github.com/owncast/owncast/activitypub/resolvers"
 	log "github.com/sirupsen/logrus"
@@ -11,7 +12,7 @@ import (
 
 func handleUpdateRequest(c context.Context, activity vocab.ActivityStreamsUpdate) error {
 	// We only care about update events to followers.
-	if !activity.GetActivityStreamsObject().At(0).IsActivityStreamsPerson() {
+	if !apmodels.IsFirstObjectActivityStreamsPerson(activity.GetActivityStreamsObject()) {
 		return nil
 	}
 
@@ -21,5 +22,5 @@ func handleUpdateRequest(c context.Context, activity vocab.ActivityStreamsUpdate
 		return err
 	}
 
-	return persistence.UpdateFollower(actor.ActorIri.String(), actor.Inbox.String(), actor.Name, actor.FullUsername, actor.Image.String())
+	return persistence.UpdateFollower(actor.ActorIriString(), actor.InboxString(), actor.Name, actor.FullUsername, actor.ImageString())
 }