minor #15233 Update login_link.rst (Mis0u)

This PR was merged into the 5.2 branch.

Discussion
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Update login_link.rst

I propose this change to manage the case of the link is invalid

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Commits
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3780af2 Update login_link.rst

Author: javiereguiluz

security/login_link.rst

@@ -739,3 +739,5 @@ Then, configure this service ID as the ``success_handler``:
                 ],
             ],
         ]);
+        
+If you want to manage the failure for example the link is expires, use 'failure_handler' and implements "AuthenticationFailureHandlerInterface" instand of "AuthenticationSuccessHandlerInterface"