mail: allow PLAIN auth over non-tls connections (#3900)

This allows mattermost to use a non-tls connection with a SMTP server that
supports PLAIN auth (but not LOGIN). The go library explicitly allows PLAIN
auth over non-tls connections - https://golang.org/src/net/smtp/auth.go#L55

Fixes #2929

model/config.go

@@ -11,6 +11,7 @@ import (
 
 const (
 	CONN_SECURITY_NONE     = ""
+	CONN_SECURITY_PLAIN    = "PLAIN"
 	CONN_SECURITY_TLS      = "TLS"
 	CONN_SECURITY_STARTTLS = "STARTTLS"
 
@@ -964,7 +965,7 @@ func (o *Config) IsValid() *AppError {
 		return NewLocAppError("Config.IsValid", "model.config.is_valid.file_salt.app_error", nil, "")
 	}
 
-	if !(o.EmailSettings.ConnectionSecurity == CONN_SECURITY_NONE || o.EmailSettings.ConnectionSecurity == CONN_SECURITY_TLS || o.EmailSettings.ConnectionSecurity == CONN_SECURITY_STARTTLS) {
+	if !(o.EmailSettings.ConnectionSecurity == CONN_SECURITY_NONE || o.EmailSettings.ConnectionSecurity == CONN_SECURITY_TLS || o.EmailSettings.ConnectionSecurity == CONN_SECURITY_STARTTLS || o.EmailSettings.ConnectionSecurity == CONN_SECURITY_PLAIN) {
 		return NewLocAppError("Config.IsValid", "model.config.is_valid.email_security.app_error", nil, "")
 	}
 

utils/mail.go

@@ -52,8 +52,6 @@ func newSMTPClient(conn net.Conn, config *model.Config) (*smtp.Client, *model.Ap
 		l4g.Error(T("utils.mail.new_client.open.error"), err)
 		return nil, model.NewLocAppError("SendMail", "utils.mail.connect_smtp.open_tls.app_error", nil, err.Error())
 	}
-	// GO does not support plain auth over a non encrypted connection.
-	// so if not tls then no auth
 	auth := smtp.PlainAuth("", config.EmailSettings.SMTPUsername, config.EmailSettings.SMTPPassword, config.EmailSettings.SMTPServer+":"+config.EmailSettings.SMTPPort)
 	if config.EmailSettings.ConnectionSecurity == model.CONN_SECURITY_TLS {
 		if err = c.Auth(auth); err != nil {
@@ -68,6 +66,11 @@ func newSMTPClient(conn net.Conn, config *model.Config) (*smtp.Client, *model.Ap
 		if err = c.Auth(auth); err != nil {
 			return nil, model.NewLocAppError("SendMail", "utils.mail.new_client.auth.app_error", nil, err.Error())
 		}
+	} else if config.EmailSettings.ConnectionSecurity == model.CONN_SECURITY_PLAIN {
+		// note: go library only supports PLAIN auth over non-tls connections
+		if err = c.Auth(auth); err != nil {
+			return nil, model.NewLocAppError("SendMail", "utils.mail.new_client.auth.app_error", nil, err.Error())
+		}
 	}
 	return c, nil
 }

webapp/components/admin_console/connection_security_dropdown_setting.jsx

@@ -27,6 +27,20 @@ const CONNECTION_SECURITY_HELP_TEXT = (
                     />
                 </td>
             </tr>
+            <tr>
+                <td>
+                    <FormattedMessage
+                        id='admin.connectionSecurityPlain'
+                        defaultMessage='PLAIN'
+                    />
+                </td>
+                <td>
+                    <FormattedMessage
+                        id='admin.connectionSecurityPlainDescription'
+                        defaultMessage='Mattermost will connect and authenticate over an unsecure connection.'
+                    />
+                </td>
+            </tr>
             <tr>
                 <td>
                     <FormattedMessage
@@ -66,6 +80,7 @@ export default class ConnectionSecurityDropdownSetting extends React.Component {
                 id='connectionSecurity'
                 values={[
                     {value: '', text: Utils.localizeMessage('admin.connectionSecurityNone', 'None')},
+                    {value: 'PLAIN', text: Utils.localizeMessage('admin.connectionSecurityPlain')},
                     {value: 'TLS', text: Utils.localizeMessage('admin.connectionSecurityTls', 'TLS (Recommended)')},
                     {value: 'STARTTLS', text: Utils.localizeMessage('admin.connectionSecurityStart')}
                 ]}

webapp/i18n/en.json

@@ -199,6 +199,8 @@
   "admin.compliance_table.userId": "Requested By",
   "admin.connectionSecurityNone": "None",
   "admin.connectionSecurityNoneDescription": "Mattermost will connect over an unsecure connection.",
+  "admin.connectionSecurityPlain": "PLAIN",
+  "admin.connectionSecurityPlainDescription": "Mattermost will connect and authenticate over an unsecure connection.",
   "admin.connectionSecurityStart": "STARTTLS",
   "admin.connectionSecurityStartDescription": "Takes an existing insecure connection and attempts to upgrade it to a secure connection using TLS.",
   "admin.connectionSecurityTest": "Test Connection",