End session endpoint ignores state parameter.

[BennieCopeland]

According to the specification, the state parameter is an:

Opaque value used by the RP to maintain state between the logout request and the callback to the endpoint specified by the post_logout_redirect_uri parameter. If included in the logout request, the OP passes this value back to the RP using the state parameter when redirecting the User Agent back to the RP.

The mock-oauth2-server is not returning the opaque value to the RP, which in my case is preventing my application from completing the logout sequence.