This option should contain a comma separated list of options you can override. These options can then be changed specifically in various directories by adding them to a mc_access file. The default value of this option is "*" which tells TinyMCE to allow override of all options.
Example of usage in the config.php file:
$mcFileManagerConfig['authenticator.allow_override'] = "authenticator";
Example of usage in a mc_access file:
# Override something
authenticator=SomeAuthenticator
# Allow override
authenticator.allow_override=authenticator