minor symfony#13834 Update authentication.rst (zairigimad)

This PR was submitted for the 5.0 branch but it was merged into the 4.4 branch instead.

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Update authentication.rst

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9f2f0f1 Update authentication.rst

Author: javiereguiluz

components/security/authentication.rst

@@ -197,7 +197,7 @@ Creating a custom Password Encoder
 There are many built-in password encoders. But if you need to create your
 own, it needs to follow these rules:
 
-#. The class must implement :class:`Symfony\\Component\\Security\\Core\\Encoder\\PasswordEncoderInterface`;
+#. The class must implement :class:`Symfony\\Component\\Security\\Core\\Encoder\\PasswordEncoderInterface`; or extend :class:`Symfony\\Component\\Security\\Core\\Encoder\\BasePasswordEncoder`;
 
 #. The implementations of
    :method:`Symfony\\Component\\Security\\Core\\Encoder\\PasswordEncoderInterface::encodePassword`