Trying to build sssd 1.16.0 I hit the following during the configure step; checking for JANSSON... no checking jansson.h usability... no checking jansson.h presence... no checking for jansson.h... no configure: error: You must have the header file jansson.h installed to build sssd with secrets and KCM responder. If you want to build sssd without these responders then specify --without-secrets --without-kcm when running configure. Manually installing dev-libs/jansson and I could build sssd 1.16.0.
Sorry, the recent dependency came in from an overlay with sssd 1.16, gentoo has only up to 1.13.1... Silly me....