Allow blocking some email domains from registering an account (#14667)

Gitea allows to whitelist email domains so that only email addresses from certain domains are allowed to register an account, but does not currently allows to do the opposite: blacklisting email domains so that addresses from certain domains are *forbidden* to register an account.

The idea has been briefly mentioned in the discussion about issue #6350, but never implemented. This PR does that.

The rationale is that, in my experience of running a Gitea instance, *a single email domain* is responsible for *most* of the spam accounts, and for *all* of the spam accounts that manage to get past the email confirmation step. So on top of the other spam mitigation measures already available (email confirmation, CAPTCHA, etc.), having the option to block a particularly annoying domain would be helpful.

close #13628

custom/conf/app.example.ini

@@ -617,6 +617,8 @@ REGISTER_MANUAL_CONFIRM = false
 ; List of domain names that are allowed to be used to register on a Gitea instance
 ; gitea.io,example.com
 EMAIL_DOMAIN_WHITELIST =
+; Comma-separated list of domain names that are not allowed to be used to register on a Gitea instance
+EMAIL_DOMAIN_BLOCKLIST =
 ; Disallow registration, only allow admins to create accounts.
 DISABLE_REGISTRATION = false
 ; Allow registration only using third-party services, it works only when DISABLE_REGISTRATION is false

docs/content/doc/advanced/config-cheat-sheet.en-us.md

@@ -466,6 +466,7 @@ relation to port exhaustion.
 - `DEFAULT_ALLOW_ONLY_CONTRIBUTORS_TO_TRACK_TIME`: **true**: Only allow users with write permissions to track time.
 - `EMAIL_DOMAIN_WHITELIST`: **\<empty\>**: If non-empty, list of domain names that can only be used to register
   on this instance.
+- `EMAIL_DOMAIN_BLOCKLIST`: **\<empty\>**: If non-empty, list of domain names that cannot be used to register on this instance
 - `SHOW_REGISTRATION_BUTTON`: **! DISABLE\_REGISTRATION**: Show Registration Button
 - `SHOW_MILESTONES_DASHBOARD_PAGE`: **true** Enable this to show the milestones dashboard page - a view of all the user's milestones
 - `AUTO_WATCH_NEW_REPOS`: **true**: Enable this to let all organisation users watch new repos when they are created

docs/content/doc/help/faq.en-us.md

@@ -120,13 +120,14 @@ For more information, refer to Gitea's [API docs]({{< relref "doc/developers/api
 
 There are multiple things you can combine to prevent spammers.
 
-1. By only whitelisting certain domains with OpenID (see below)
-2. Setting `ENABLE_CAPTCHA` to `true` in your `app.ini` and properly configuring `RECAPTCHA_SECRET` and `RECAPTCHA_SITEKEY`
-3. Settings `DISABLE_REGISTRATION` to `true` and creating new users via the [CLI]({{< relref "doc/usage/command-line.en-us.md" >}}), [API]({{< relref "doc/developers/api-usage.en-us.md" >}}), or Gitea's Admin UI
+1. By whitelisting or blocklisting certain email domains
+2. By only whitelisting certain domains with OpenID (see below)
+3. Setting `ENABLE_CAPTCHA` to `true` in your `app.ini` and properly configuring `RECAPTCHA_SECRET` and `RECAPTCHA_SITEKEY`
+4. Settings `DISABLE_REGISTRATION` to `true` and creating new users via the [CLI]({{< relref "doc/usage/command-line.en-us.md" >}}), [API]({{< relref "doc/developers/api-usage.en-us.md" >}}), or Gitea's Admin UI
 
-### Only allow certain email domains
+### Only allow/block certain email domains
 
-You can configure `EMAIL_DOMAIN_WHITELIST` in your app.ini under `[service]`
+You can configure `EMAIL_DOMAIN_WHITELIST` or `EMAIL_DOMAIN_BLOCKLIST` in your app.ini under `[service]`
 
 ### Only allow/block certain OpenID providers
 

modules/forms/user_form.go

@@ -95,23 +95,21 @@ func (f *RegisterForm) Validate(req *http.Request, errs binding.Errors) binding.
 	return middleware.Validate(errs, ctx.Data, f, ctx.Locale)
 }
 
-// IsEmailDomainWhitelisted validates that the email address
-// provided by the user matches what has been configured .
-// If the domain whitelist from the config is empty, it marks the
-// email as whitelisted
-func (f RegisterForm) IsEmailDomainWhitelisted() bool {
-	if len(setting.Service.EmailDomainWhitelist) == 0 {
-		return true
+// IsEmailDomainListed checks whether the domain of an email address
+// matches a list of domains
+func IsEmailDomainListed(list []string, email string) bool {
+	if len(list) == 0 {
+		return false
 	}
 
-	n := strings.LastIndex(f.Email, "@")
+	n := strings.LastIndex(email, "@")
 	if n <= 0 {
 		return false
 	}
 
-	domain := strings.ToLower(f.Email[n+1:])
+	domain := strings.ToLower(email[n+1:])
 
-	for _, v := range setting.Service.EmailDomainWhitelist {
+	for _, v := range list {
 		if strings.ToLower(v) == domain {
 			return true
 		}
@@ -120,6 +118,19 @@ func (f RegisterForm) IsEmailDomainWhitelisted() bool {
 	return false
 }
 
+// IsEmailDomainAllowed validates that the email address
+// provided by the user matches what has been configured .
+// The email is marked as allowed if it matches any of the
+// domains in the whitelist or if it doesn't match any of
+// domains in the blocklist, if any such list is not empty.
+func (f RegisterForm) IsEmailDomainAllowed() bool {
+	if len(setting.Service.EmailDomainWhitelist) == 0 {
+		return !IsEmailDomainListed(setting.Service.EmailDomainBlocklist, f.Email)
+	}
+
+	return IsEmailDomainListed(setting.Service.EmailDomainWhitelist, f.Email)
+}
+
 // MustChangePasswordForm form for updating your password after account creation
 // by an admin
 type MustChangePasswordForm struct {

modules/forms/user_form_test.go

@@ -12,17 +12,17 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestRegisterForm_IsDomainWhiteList_Empty(t *testing.T) {
+func TestRegisterForm_IsDomainAllowed_Empty(t *testing.T) {
 	_ = setting.Service
 
 	setting.Service.EmailDomainWhitelist = []string{}
 
 	form := RegisterForm{}
 
-	assert.True(t, form.IsEmailDomainWhitelisted())
+	assert.True(t, form.IsEmailDomainAllowed())
 }
 
-func TestRegisterForm_IsDomainWhiteList_InvalidEmail(t *testing.T) {
+func TestRegisterForm_IsDomainAllowed_InvalidEmail(t *testing.T) {
 	_ = setting.Service
 
 	setting.Service.EmailDomainWhitelist = []string{"gitea.io"}
@@ -37,11 +37,11 @@ func TestRegisterForm_IsDomainWhiteList_InvalidEmail(t *testing.T) {
 	for _, v := range tt {
 		form := RegisterForm{Email: v.email}
 
-		assert.False(t, form.IsEmailDomainWhitelisted())
+		assert.False(t, form.IsEmailDomainAllowed())
 	}
 }
 
-func TestRegisterForm_IsDomainWhiteList_ValidEmail(t *testing.T) {
+func TestRegisterForm_IsDomainAllowed_WhitelistedEmail(t *testing.T) {
 	_ = setting.Service
 
 	setting.Service.EmailDomainWhitelist = []string{"gitea.io"}
@@ -59,6 +59,28 @@ func TestRegisterForm_IsDomainWhiteList_ValidEmail(t *testing.T) {
 	for _, v := range tt {
 		form := RegisterForm{Email: v.email}
 
-		assert.Equal(t, v.valid, form.IsEmailDomainWhitelisted())
+		assert.Equal(t, v.valid, form.IsEmailDomainAllowed())
+	}
+}
+
+func TestRegisterForm_IsDomainAllowed_BlocklistedEmail(t *testing.T) {
+	_ = setting.Service
+
+	setting.Service.EmailDomainWhitelist = []string{}
+	setting.Service.EmailDomainBlocklist = []string{"gitea.io"}
+
+	tt := []struct {
+		email string
+		valid bool
+	}{
+		{"security@gitea.io", false},
+		{"security@gitea.example", true},
+		{"hdudhdd", true},
+	}
+
+	for _, v := range tt {
+		form := RegisterForm{Email: v.email}
+
+		assert.Equal(t, v.valid, form.IsEmailDomainAllowed())
 	}
 }

modules/setting/service.go

@@ -20,6 +20,7 @@ var Service struct {
 	RegisterEmailConfirm                    bool
 	RegisterManualConfirm                   bool
 	EmailDomainWhitelist                    []string
+	EmailDomainBlocklist                    []string
 	DisableRegistration                     bool
 	AllowOnlyExternalRegistration           bool
 	ShowRegistrationButton                  bool
@@ -72,6 +73,7 @@ func newService() {
 		Service.RegisterManualConfirm = false
 	}
 	Service.EmailDomainWhitelist = sec.Key("EMAIL_DOMAIN_WHITELIST").Strings(",")
+	Service.EmailDomainBlocklist = sec.Key("EMAIL_DOMAIN_BLOCKLIST").Strings(",")
 	Service.ShowRegistrationButton = sec.Key("SHOW_REGISTRATION_BUTTON").MustBool(!(Service.DisableRegistration || Service.AllowOnlyExternalRegistration))
 	Service.ShowMilestonesDashboardPage = sec.Key("SHOW_MILESTONES_DASHBOARD_PAGE").MustBool(true)
 	Service.RequireSignInView = sec.Key("REQUIRE_SIGNIN_VIEW").MustBool()

routers/user/auth.go

@@ -1129,7 +1129,7 @@ func SignUpPost(ctx *context.Context) {
 		}
 	}
 
-	if !form.IsEmailDomainWhitelisted() {
+	if !form.IsEmailDomainAllowed() {
 		ctx.RenderWithErr(ctx.Tr("auth.email_domain_blacklisted"), tplSignUp, &form)
 		return
 	}