diff --git a/src/lib/PHPMailer/OAuthTokenProvider.php b/src/lib/PHPMailer/OAuthTokenProvider.php
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+++ b/src/lib/PHPMailer/OAuthTokenProvider.php
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+<?php
+
+/**
+ * PHPMailer - PHP email creation and transport class.
+ * PHP Version 5.5.
+ *
+ * @see https://github.com/PHPMailer/PHPMailer/ The PHPMailer GitHub project
+ *
+ * @author    Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
+ * @author    Jim Jagielski (jimjag) <jimjag@gmail.com>
+ * @author    Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
+ * @author    Brent R. Matzelle (original founder)
+ * @copyright 2012 - 2020 Marcus Bointon
+ * @copyright 2010 - 2012 Jim Jagielski
+ * @copyright 2004 - 2009 Andy Prevost
+ * @license   http://www.gnu.org/copyleft/lesser.html GNU Lesser General Public License
+ * @note      This program is distributed in the hope that it will be useful - WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+namespace PHPMailer\PHPMailer;
+
+/**
+ * OAuthTokenProvider - OAuth2 token provider interface.
+ * Provides base64 encoded OAuth2 auth strings for SMTP authentication.
+ *
+ * @see     OAuth
+ * @see     SMTP::authenticate()
+ *
+ * @author  Peter Scopes (pdscopes)
+ * @author  Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
+ */
+interface OAuthTokenProvider
+{
+    /**
+     * Generate a base64-encoded OAuth token ensuring that the access token has not expired.
+     * The string to be base 64 encoded should be in the form:
+     * "user=<user_email_address>\001auth=Bearer <access_token>\001\001"
+     *
+     * @return string
+     */
+    public function getOauth64();
+}