Added external, XOAuth2 and OAuthBearer auth methods

src/ManageSieve/Auth/ExternalAuthMechanism.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace PhpSieveManager\ManageSieve\Auth;
+
+use PhpSieveManager\ManageSieve\SieveCommand;
+
+class ExternalAuthMechanism extends BaseAuthMechanism
+{
+    /**
+     * SASL Authentication
+     *
+     * @return SieveCommand
+     */
+    function parse()
+    {
+        $args = base64_encode($this->username);
+        return new SieveCommand(
+            "AUTHENTICATE",
+            ['"EXTERNAL"', '"'.$args.'"']
+        );
+    }
+}

src/ManageSieve/Auth/OauthbearerAuthMechanism.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace PhpSieveManager\ManageSieve\Auth;
+
+use PhpSieveManager\ManageSieve\SieveCommand;
+
+class OauthbearerAuthMechanism extends BaseAuthMechanism
+{
+    /**
+     * SASL Authentication
+     *
+     * @return SieveCommand
+     */
+    function parse()
+    {
+        $args = base64_encode("n,a={$this->username}\001auth=$this->password\001\001");
+        return new SieveCommand(
+            "AUTHENTICATE",
+            ['"OAUTHBEARER"', '"'.$args.'"']
+        );
+    }
+}

src/ManageSieve/Auth/Xoauth2AuthMechanism.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace PhpSieveManager\ManageSieve\Auth;
+
+use PhpSieveManager\ManageSieve\SieveCommand;
+
+class Xoauth2AuthMechanism extends BaseAuthMechanism
+{
+    /**
+     * SASL Authentication
+     *
+     * @return SieveCommand
+     */
+    function parse()
+    {
+        $args = base64_encode("user={$this->username}\001auth={$this->password}\001\001");
+        return new SieveCommand(
+            "AUTHENTICATE",
+            ['"XOAUTH2"', '"'.$args.'"']
+        );
+    }
+}

src/ManageSieve/Client.php

@@ -14,7 +14,7 @@
  */
 class Client implements SieveClient
 {
-    const SUPPORTED_AUTH_MECHS = ["DIGEST-MD5", "PLAIN", "LOGIN"];
+    const SUPPORTED_AUTH_MECHS = ["DIGEST-MD5", "PLAIN", "LOGIN", "EXTERNAL", "OAUTHBEARER", "XOAUTH2"];
     const KNOWN_CAPABILITIES = ["IMPLEMENTATION", "SASL", "SIEVE", "STARTTLS", "NOTIFY", "LANGUAGE", "VERSION"];
 
     private $readSize = 4096;