Advertise a valid IPPS certificate for AirPrint

Containerfile

@@ -27,7 +27,8 @@ ENV DEBIAN_FRONTEND=noninteractive
 # --- Task 3.1: base system, CUPS, Avahi, DBus and conversion filters -------
 # cups-filters provides the PDF/PWG/URF -> PostScript filters used for
 # driverless clients (AirPrint/IPP Everywhere). Ghostscript and Poppler supply
-# the underlying converters.
+# the underlying converters, openssl is used by the entrypoint to generate the
+# IPPS certificate that AirPrint clients (macOS/iOS) validate.
 RUN apt-get update \
     && apt-get install -y --no-install-recommends \
         cups \
@@ -42,6 +43,7 @@ RUN apt-get update \
         ghostscript \
         poppler-utils \
         ca-certificates \
+        openssl \
     && rm -rf /var/lib/apt/lists/*
 
 # --- Task 3.2: install the BR-Script3 PostScript PPD -----------------------