denormalise PreAuthKey tags (#2155)

this commit denormalises the Tags related to a Pre auth key
back onto the preauthkey table and struct as a string list.

There was not really any real normalisation here as we just added
a bunch of duplicate tags with new IDs and preauthkeyIDs, lots of
GORM cermony but no actual advantage.

This work is the start to fixup tags which currently are not working
as they should.

Updates #1369

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/types/preauth_key.go

@@ -16,21 +16,14 @@ type PreAuthKey struct {
 	UserID    uint
 	User      User `gorm:"constraint:OnDelete:CASCADE;"`
 	Reusable  bool
-	Ephemeral bool               `gorm:"default:false"`
-	Used      bool               `gorm:"default:false"`
-	ACLTags   []PreAuthKeyACLTag `gorm:"constraint:OnDelete:CASCADE;"`
+	Ephemeral bool     `gorm:"default:false"`
+	Used      bool     `gorm:"default:false"`
+	Tags      []string `gorm:"serializer:json"`
 
 	CreatedAt  *time.Time
 	Expiration *time.Time
 }
 
-// PreAuthKeyACLTag describes an autmatic tag applied to a node when registered with the associated PreAuthKey.
-type PreAuthKeyACLTag struct {
-	ID           uint64 `gorm:"primary_key"`
-	PreAuthKeyID uint64
-	Tag          string
-}
-
 func (key *PreAuthKey) Proto() *v1.PreAuthKey {
 	protoKey := v1.PreAuthKey{
 		User:      key.User.Name,
@@ -39,7 +32,7 @@ func (key *PreAuthKey) Proto() *v1.PreAuthKey {
 		Ephemeral: key.Ephemeral,
 		Reusable:  key.Reusable,
 		Used:      key.Used,
-		AclTags:   make([]string, len(key.ACLTags)),
+		AclTags:   key.Tags,
 	}
 
 	if key.Expiration != nil {
@@ -50,9 +43,5 @@ func (key *PreAuthKey) Proto() *v1.PreAuthKey {
 		protoKey.CreatedAt = timestamppb.New(*key.CreatedAt)
 	}
 
-	for idx := range key.ACLTags {
-		protoKey.AclTags[idx] = key.ACLTags[idx].Tag
-	}
-
 	return &protoKey
 }