diff --git a/Sieve.php b/Sieve.php
index 26e02f7..44be84d 100644
--- a/Sieve.php
+++ b/Sieve.php
@@ -101,7 +101,8 @@ class Net_Sieve
         'PLAIN' ,
         'LOGIN',
         'GSSAPI',
-        'XOAUTH2'
+        'XOAUTH2',
+        'OAUTHBEARER'
     );
 
     /**
@@ -703,6 +704,9 @@ function _cmdAuthenticate($uid, $pwd, $userMethod = null, $euser = '')
         case 'XOAUTH2':
             $result = $this->_authXOAUTH2($uid, $pwd, $euser);
             break;
+        case 'OAUTHBEARER':
+            $result = $this->_authOAUTHBEARER($uid, $pwd, $euser);
+            break;
         default :
             $result = $this->_pear->raiseError(
                 $method . ' is not a supported authentication method'
@@ -946,6 +950,29 @@ function _authXOAUTH2($user, $token, $euser)
         return $this->_sendCmd("AUTHENTICATE \"XOAUTH2\" \"$auth\"");
     }
 
+    /**
+     * Authenticates the user using the OAUTHBEARER method.
+     *
+     * @param string $user  The userid to authenticate as.
+     * @param string $token The token to authenticate with.
+     * @param string $euser The effective uid to authenticate as.
+     *
+     * @return void
+     *
+     * @see https://www.rfc-editor.org/rfc/rfc7628.html
+     * @since 1.4.7
+     */
+    function _authOAUTHBEARER($user, $token, $euser)
+    {
+        // default to $user if $euser is not set
+        if (! $euser) {
+            $euser = $user;
+        }
+
+        $auth = base64_encode("n,a=$euser\001auth=$token\001\001");
+        return $this->_sendCmd("AUTHENTICATE \"OAUTHBEARER\" \"$auth\"");
+    }
+
     /**
      * Removes a script from the server.
      *