forced authentication attribute not being used

[Jeff McCullough]

We are using the  authn/External module in 4.1.4. I have the property setting in authn.properties to allow forced Authentication:
idp.authn.External.forcedAuthenticationSupported = true

but it doesn’t appear to use it. I see the following error in the logs:

DEBUG [net.shibboleth.idp.authn.impl.FilterFlowsByForcedAuthn:79] - Profile Action FilterFlowsByForcedAuthn: Removing flow authn/External, it does not support forced authentication

Any advice on how to troubleshoot? The documentation suggests this is the way to turn on support for forced authentication. 

Thank you,
Jeff
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