Save initial signup information for users to aid in spam prevention (#31852)

This will allow instance admins to view signup pattern patterns for
public instances. It is modelled after discourse, mastodon, and
MediaWiki's approaches.

Note: This has privacy implications, but as the above-stated open-source
projects take this approach, especially MediaWiki, which I have no doubt
looked into this thoroughly, it is likely okay for us, too. However, I
would be appreciative of any feedback on how this could be improved.

---------

Co-authored-by: Giteabot <teabot@gitea.io>

models/user/setting_keys.go

@@ -14,4 +14,8 @@ const (
 	UserActivityPubPrivPem = "activitypub.priv_pem"
 	// UserActivityPubPubPem is user's public key
 	UserActivityPubPubPem = "activitypub.pub_pem"
+	// SignupIP is the IP address that the user signed up with
+	SignupIP = "signup.ip"
+	// SignupUserAgent is the user agent that the user signed up with
+	SignupUserAgent = "signup.user_agent"
 )

models/user/user.go

@@ -150,6 +150,14 @@ type User struct {
 	KeepActivityPrivate bool   `xorm:"NOT NULL DEFAULT false"`
 }
 
+// Meta defines the meta information of a user, to be stored in the K/V table
+type Meta struct {
+	// Store the initial registration of the user, to aid in spam prevention
+	// Ensure that one IP isn't creating many accounts (following mediawiki approach)
+	InitialIP        string
+	InitialUserAgent string
+}
+
 func init() {
 	db.RegisterModel(new(User))
 }
@@ -615,17 +623,17 @@ type CreateUserOverwriteOptions struct {
 }
 
 // CreateUser creates record of a new user.
-func CreateUser(ctx context.Context, u *User, overwriteDefault ...*CreateUserOverwriteOptions) (err error) {
-	return createUser(ctx, u, false, overwriteDefault...)
+func CreateUser(ctx context.Context, u *User, meta *Meta, overwriteDefault ...*CreateUserOverwriteOptions) (err error) {
+	return createUser(ctx, u, meta, false, overwriteDefault...)
 }
 
 // AdminCreateUser is used by admins to manually create users
-func AdminCreateUser(ctx context.Context, u *User, overwriteDefault ...*CreateUserOverwriteOptions) (err error) {
-	return createUser(ctx, u, true, overwriteDefault...)
+func AdminCreateUser(ctx context.Context, u *User, meta *Meta, overwriteDefault ...*CreateUserOverwriteOptions) (err error) {
+	return createUser(ctx, u, meta, true, overwriteDefault...)
 }
 
 // createUser creates record of a new user.
-func createUser(ctx context.Context, u *User, createdByAdmin bool, overwriteDefault ...*CreateUserOverwriteOptions) (err error) {
+func createUser(ctx context.Context, u *User, meta *Meta, createdByAdmin bool, overwriteDefault ...*CreateUserOverwriteOptions) (err error) {
 	if err = IsUsableUsername(u.Name); err != nil {
 		return err
 	}
@@ -745,6 +753,22 @@ func createUser(ctx context.Context, u *User, createdByAdmin bool, overwriteDefa
 		return err
 	}
 
+	if setting.RecordUserSignupMetadata {
+		// insert initial IP and UserAgent
+		if err = SetUserSetting(ctx, u.ID, SignupIP, meta.InitialIP); err != nil {
+			return err
+		}
+
+		// trim user agent string to a reasonable length, if necessary
+		userAgent := strings.TrimSpace(meta.InitialUserAgent)
+		if len(userAgent) > 255 {
+			userAgent = userAgent[:255]
+		}
+		if err = SetUserSetting(ctx, u.ID, SignupUserAgent, userAgent); err != nil {
+			return err
+		}
+	}
+
 	// insert email address
 	if err := db.Insert(ctx, &EmailAddress{
 		UID:         u.ID,

models/user/user_test.go

@@ -227,7 +227,7 @@ func TestCreateUserInvalidEmail(t *testing.T) {
 		MustChangePassword: false,
 	}
 
-	err := user_model.CreateUser(db.DefaultContext, user)
+	err := user_model.CreateUser(db.DefaultContext, user, &user_model.Meta{})
 	assert.Error(t, err)
 	assert.True(t, user_model.IsErrEmailCharIsNotSupported(err))
 }
@@ -241,7 +241,7 @@ func TestCreateUserEmailAlreadyUsed(t *testing.T) {
 	user.Name = "testuser"
 	user.LowerName = strings.ToLower(user.Name)
 	user.ID = 0
-	err := user_model.CreateUser(db.DefaultContext, user)
+	err := user_model.CreateUser(db.DefaultContext, user, &user_model.Meta{})
 	assert.Error(t, err)
 	assert.True(t, user_model.IsErrEmailAlreadyUsed(err))
 }
@@ -258,7 +258,7 @@ func TestCreateUserCustomTimestamps(t *testing.T) {
 	user.ID = 0
 	user.Email = "unique@example.com"
 	user.CreatedUnix = creationTimestamp
-	err := user_model.CreateUser(db.DefaultContext, user)
+	err := user_model.CreateUser(db.DefaultContext, user, &user_model.Meta{})
 	assert.NoError(t, err)
 
 	fetched, err := user_model.GetUserByID(context.Background(), user.ID)
@@ -283,7 +283,7 @@ func TestCreateUserWithoutCustomTimestamps(t *testing.T) {
 	user.Email = "unique@example.com"
 	user.CreatedUnix = 0
 	user.UpdatedUnix = 0
-	err := user_model.CreateUser(db.DefaultContext, user)
+	err := user_model.CreateUser(db.DefaultContext, user, &user_model.Meta{})
 	assert.NoError(t, err)
 
 	timestampEnd := time.Now().Unix()