[main]: install curl in dockerfile

Dockerfile

@@ -2,6 +2,7 @@ FROM rocker/shiny:4.4.0
 
 # System dependencies commonly required by R packages
 RUN apt-get update && apt-get install -y \
+    curl \
     libcurl4-openssl-dev \
     libssl-dev \
     libxml2-dev \
@@ -22,7 +23,15 @@ COPY . /srv/shiny-server/
 
 # Prevent renv attempting to use pak
 ENV RENV_CONFIG_PAK_ENABLED=FALSE
-ENV CFLAGS=-Wno-error=format-security
+ENV RENV_DOWNLOAD_METHOD=libcurl
+
+# Some CRAN packages in this lockfile fail under Ubuntu hardening defaults
+# because -Werror=format-security turns benign warnings into build failures.
+RUN for f in /usr/local/lib/R/etc/Makeconf /usr/lib/R/etc/Makeconf; do \
+      if [ -f "$f" ]; then \
+        sed -i 's/-Werror=format-security/-Wno-error=format-security/g' "$f"; \
+      fi; \
+    done
 
 # Install renv and restore project packages
 RUN R --vanilla -e "install.packages('renv', repos='https://cran.rstudio.com')" && \