As of 3.4

• GuardAuthenticatorInterface is deprecated and will be removed in 4.0, references should be updated to use AuthenticatorInterface instead (starting from 3.4);
• AuthenticatorInterface introduces a supports() method used to skip authenticators which are not able to process authentication from the given request, any authenticator must implement it
• GuardAuthenticatorInterface::getCredentials() returning null causes the authenticator to be skipped. This behavior has been removed in the new AuthenticatorInterface, returning null from AuthenticatorInterface::getCredentials() throws an \UnexpectedValueException exception (false should be returned from supports() instead)

Code PR: symfony/symfony#16835