And follow requests work!

Who knew that Mastodon would set the accept target's object id to the
internal one?

But also, I am of the opinion that this is a bug on our side when
translating the activity to AP

web/public/api/activitypub/inbox.go

@@ -387,6 +387,7 @@ func handleAccept(w http.ResponseWriter, r *http.Request, object map[string]any)
 	log := hlog.FromRequest(r)
 	rawTarget, ok := object["object"]
 	if !ok {
+		log.Debug().Msg("Rejecting accept, missing object")
 		_ = webutils.ProblemDetails(
 			w,
 			http.StatusBadRequest,
@@ -397,7 +398,6 @@ func handleAccept(w http.ResponseWriter, r *http.Request, object map[string]any)
 		)
 		return true
 	}
-	// FIXME: Also handle other undo cases, such as follows
 	var targetObjectId string
 	// I *think* the spec says that this must be an object. Not sure though
 	switch target := rawTarget.(type) {
@@ -406,7 +406,20 @@ func handleAccept(w http.ResponseWriter, r *http.Request, object map[string]any)
 	case map[string]any:
 		objType, ok := target["type"].(string)
 		// TODO: Ensure accept is only used for follows
-		if !ok || objType != "Follow" {
+		if !ok {
+			log.Debug().Msg("Rejecting accept, missing embedded object data")
+			_ = webutils.ProblemDetails(
+				w,
+				http.StatusBadRequest,
+				"/errors/bad-request-data",
+				"Bad activity data",
+				other.IntoPointer(`Target object must contain a type field`),
+				nil,
+			)
+			return true
+		}
+		if objType != "Follow" {
+			log.Debug().Msg("Rejecting accept, bad object type")
 			_ = webutils.ProblemDetails(
 				w,
 				http.StatusBadRequest,
@@ -419,6 +432,7 @@ func handleAccept(w http.ResponseWriter, r *http.Request, object map[string]any)
 		}
 		targetObjectId, ok = target["id"].(string)
 		if !ok {
+			log.Debug().Msg("Rejecting accept, missing object id")
 			_ = webutils.ProblemDetails(
 				w,
 				http.StatusBadRequest,
@@ -430,6 +444,7 @@ func handleAccept(w http.ResponseWriter, r *http.Request, object map[string]any)
 			return true
 		}
 	default:
+		log.Debug().Msg("Rejecting accept, missing object field")
 		_ = webutils.ProblemDetails(
 			w,
 			http.StatusBadRequest,
@@ -440,22 +455,29 @@ func handleAccept(w http.ResponseWriter, r *http.Request, object map[string]any)
 		)
 		return true
 	}
-	internalIdMatch := objectIdRegex.FindStringSubmatch(targetObjectId)
+	var internalId string
-	if len(internalIdMatch) != 2 {
+	if strings.HasPrefix(targetObjectId, "http") {
-		_ = webutils.ProblemDetails(
+		internalIdMatch := objectIdRegex.FindStringSubmatch(targetObjectId)
-			w,
+		if len(internalIdMatch) != 2 {
-			http.StatusBadRequest,
+			log.Debug().Msg("Rejecting accept, objectIdRegex didn't match")
-			"/errors/bad-request-data",
+			_ = webutils.ProblemDetails(
-			"Bad activity data",
+				w,
-			other.IntoPointer(`Request data target object is not internal id`),
+				http.StatusBadRequest,
-			nil,
+				"/errors/bad-request-data",
-		)
+				"Bad activity data",
-		return true
+				other.IntoPointer(`Request data target object is not internal id`),
+				nil,
+			)
+			return true
+		}
+		internalId = internalIdMatch[1]
+	} else {
+		internalId = targetObjectId
 	}
-	internalId := internalIdMatch[1]
 	followActivity, err := dbgen.Activity.Where(dbgen.Activity.Id.Eq(internalId)).First()
 	switch err {
 	case gorm.ErrRecordNotFound:
+		log.Debug().Msg("Rejecting accept, target follow activity not found")
 		_ = webutils.ProblemDetailsStatusOnly(w, http.StatusNotFound)
 		return true
 	case nil: