LDAP: Fetch attributes in Bind DN context option

This is feature is workaround for #2628 (JumpCloud) and some other services
that allow LDAP search only under BindDN user account, but not allow any LDAP
search query in logged user DN context.

Such approach is an alternative to minimal permissions security pattern for
BindDN user.

conf/locale/locale_en-US.ini

@@ -921,6 +921,7 @@ auths.attribute_username_placeholder = Leave empty to use sign-in form field val
 auths.attribute_name = First name attribute
 auths.attribute_surname = Surname attribute
 auths.attribute_mail = Email attribute
+auths.attributes_in_bind = Fetch attributes in Bind DN context
 auths.filter = User Filter
 auths.admin_filter = Admin Filter
 auths.ms_ad_sa = Ms Ad SA

modules/auth/auth_form.go

@@ -23,6 +23,7 @@ type AuthenticationForm struct {
 	AttributeName     string
 	AttributeSurname  string
 	AttributeMail     string
+	AttributesInBind  bool
 	Filter            string
 	AdminFilter       string
 	IsActive          bool

modules/auth/ldap/ldap.go

@@ -31,6 +31,7 @@ type Source struct {
 	AttributeName     string // First name attribute
 	AttributeSurname  string // Surname attribute
 	AttributeMail     string // E-mail attribute
+	AttributesInBind  bool   // fetch attributes in bind context (not user)
 	Filter            string // Query filter to validate entry
 	AdminFilter       string // Query filter to check if user is admin
 	Enabled           bool   // if this source is disabled
@@ -130,14 +131,14 @@ func (ls *Source) SearchEntry(name, passwd string, directBind bool) (string, str
 		}
 	}
 
-	log.Trace("Binding with userDN: %s", userDN)
+	if directBind || !ls.AttributesInBind {
-	err = l.Bind(userDN, passwd)
+		// binds user (checking password) before looking-up attributes in user context
+		err = bindUser(l, userDN, passwd)
 		if err != nil {
-		log.Debug("LDAP auth. failed for %s, reason: %v", userDN, err)
 			return "", "", "", "", false, false
 		}
+	}
 
-	log.Trace("Bound successfully with userDN: %s", userDN)
 	userFilter, ok := ls.sanitizedUserQuery(name)
 	if !ok {
 		return "", "", "", "", false, false
@@ -184,9 +185,28 @@ func (ls *Source) SearchEntry(name, passwd string, directBind bool) (string, str
 		}
 	}
 
+	if !directBind && ls.AttributesInBind {
+		// binds user (checking password) after looking-up attributes in BindDN context
+		err = bindUser(l, userDN, passwd)
+		if err != nil {
+			return "", "", "", "", false, false
+		}
+	}
+
 	return username_attr, name_attr, sn_attr, mail_attr, admin_attr, true
 }
 
+func bindUser(l *ldap.Conn, userDN, passwd string) error {
+	log.Trace("Binding with userDN: %s", userDN)
+	err := l.Bind(userDN, passwd)
+	if err != nil {
+		log.Debug("LDAP auth. failed for %s, reason: %v", userDN, err)
+		return err
+	}
+	log.Trace("Bound successfully with userDN: %s", userDN)
+	return err
+}
+
 func ldapDial(ls *Source) (*ldap.Conn, error) {
 	if ls.UseSSL {
 		log.Debug("Using TLS for LDAP without verifying: %v", ls.SkipVerify)

routers/admin/auths.go

@@ -81,6 +81,7 @@ func parseLDAPConfig(form auth.AuthenticationForm) *models.LDAPConfig {
 			AttributeName:     form.AttributeName,
 			AttributeSurname:  form.AttributeSurname,
 			AttributeMail:     form.AttributeMail,
+			AttributesInBind:  form.AttributesInBind,
 			Filter:            form.Filter,
 			AdminFilter:       form.AdminFilter,
 			Enabled:           true,

templates/admin/auth/edit.tmpl

@@ -79,6 +79,14 @@
 								<label for="attribute_mail">{{.i18n.Tr "admin.auths.attribute_mail"}}</label>
 								<input id="attribute_mail" name="attribute_mail" value="{{$cfg.AttributeMail}}" placeholder="e.g. mail" required>
 							</div>
+							{{if .Source.IsLDAP}}
+								<div class="inline field">
+									<div class="ui checkbox">
+										<label><strong>{{.i18n.Tr "admin.auths.attributes_in_bind"}}</strong></label>
+										<input name="attributes_in_bind" type="checkbox" {{if $cfg.AttributesInBind}}checked{{end}}>
+									</div>
+								</div>
+							{{end}}
 						{{end}}
 
 						<!-- SMTP -->