small typo:
s/instanciate/instantiate 

possible rephrase to:
Authenticator is a manager and a factory. It can consume an AuthenticationConfig object and instantiate an appropriate built-in module tuned to work with a specific server configuration, or you can provide your own custom AuthenticationModule and register it with then Authenticator. We will see an example of a custom authentication module later in the guide, where we will build a custom authentication module that goes against the popular Reddit web service.
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