Build using musl

.github/workflows/Dockerfile.ci.alpine

@@ -56,8 +56,35 @@ WORKDIR /app
 ENV UID=1000
 ENV GID=1000
 ENV USER=lldap
-RUN echo http://mirror.math.princeton.edu/pub/alpinelinux/edge/testing/ >> /etc/apk/repositories && \
-    apk add --no-cache tini ca-certificates bash gosu && \
+ENV GOSU_VERSION 1.14
+# Fetch gosu from git
+RUN set -eux; \
+	\
+	apk add --no-cache --virtual .gosu-deps \
+		ca-certificates \
+		dpkg \
+		gnupg \
+	; \
+	\
+	dpkgArch="$(dpkg --print-architecture | awk -F- '{ print $NF }')"; \
+	wget -O /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch"; \
+	wget -O /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch.asc"; \
+	\
+# verify the signature
+	export GNUPGHOME="$(mktemp -d)"; \
+	gpg --batch --keyserver hkps://keys.openpgp.org --recv-keys B42F6819007F00F88E364FD4036A9C25BF357DD4; \
+	gpg --batch --verify /usr/local/bin/gosu.asc /usr/local/bin/gosu; \
+	command -v gpgconf && gpgconf --kill all || :; \
+	rm -rf "$GNUPGHOME" /usr/local/bin/gosu.asc; \
+	\
+# clean up fetch dependencies
+	apk del --no-network .gosu-deps; \
+	\
+	chmod +x /usr/local/bin/gosu; \
+# verify that the binary works
+	gosu --version; \
+	gosu nobody true
+RUN apk add --no-cache tini ca-certificates bash && \
     addgroup -g $GID $USER && \
     adduser \
     --disabled-password \