Previously the namespace configuration did not properly set the eraseCredentialsAfterAuthentication
property on the parent AuthenticationProvider when using http@authentication-manager-ref.
Now the ProviderManager that is created by the namespace consults the original
AuthenticationManager to determine if eraseCredentialsAfterAuthentication should
be set on the wrapped instance. If the original is not a ProviderManager the
eraseCredentialsAfterAuthentication is set to false since we should not "magically"
add behavior to the custom AuthenticationManager without knowing the desired behavior.
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