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/db/db.go

@@ -3,6 +3,7 @@ package db
 import (
 	"context"
 	"database/sql"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"net/netip"
@@ -19,6 +20,7 @@ import (
 	"gorm.io/driver/postgres"
 	"gorm.io/gorm"
 	"gorm.io/gorm/logger"
+	"tailscale.com/util/set"
 )
 
 var errDatabaseNotSupported = errors.New("database type not supported")
@@ -291,7 +293,12 @@ func NewHeadscaleDatabase(
 						return err
 					}
 
-					err = tx.AutoMigrate(&types.PreAuthKeyACLTag{})
+					type preAuthKeyACLTag struct {
+						ID           uint64 `gorm:"primary_key"`
+						PreAuthKeyID uint64
+						Tag          string
+					}
+					err = tx.AutoMigrate(&preAuthKeyACLTag{})
 					if err != nil {
 						return err
 					}
@@ -413,6 +420,54 @@ func NewHeadscaleDatabase(
 				},
 				Rollback: func(db *gorm.DB) error { return nil },
 			},
+			// denormalise the ACL tags for preauth keys back onto
+			// the preauth key table. We dont normalise or reuse and
+			// it is just a bunch of work for extra work.
+			{
+				ID: "202409271400",
+				Migrate: func(tx *gorm.DB) error {
+					preauthkeyTags := map[uint64]set.Set[string]{}
+
+					type preAuthKeyACLTag struct {
+						ID           uint64 `gorm:"primary_key"`
+						PreAuthKeyID uint64
+						Tag          string
+					}
+
+					var aclTags []preAuthKeyACLTag
+					if err := tx.Find(&aclTags).Error; err != nil {
+						return err
+					}
+
+					// Store the current tags.
+					for _, tag := range aclTags {
+						if preauthkeyTags[tag.PreAuthKeyID] == nil {
+							preauthkeyTags[tag.PreAuthKeyID] = set.SetOf([]string{tag.Tag})
+						} else {
+							preauthkeyTags[tag.PreAuthKeyID].Add(tag.Tag)
+						}
+					}
+
+					// Add tags column and restore the tags.
+					_ = tx.Migrator().AddColumn(&types.PreAuthKey{}, "tags")
+					for keyID, tags := range preauthkeyTags {
+						s := tags.Slice()
+						j, err := json.Marshal(s)
+						if err != nil {
+							return err
+						}
+						if err := tx.Model(&types.PreAuthKey{}).Where("id = ?", keyID).Update("tags", string(j)).Error; err != nil {
+							return err
+						}
+					}
+
+					// Drop the old table.
+					_ = tx.Migrator().DropTable(&preAuthKeyACLTag{})
+
+					return nil
+				},
+				Rollback: func(db *gorm.DB) error { return nil },
+			},
 		},
 	)