docker: install gosu

Dockerfile

@@ -43,6 +43,36 @@ RUN cargo build --release -p lldap -p migration-tool \
 # Final image
 FROM alpine:3.14
 
+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
+
+
 WORKDIR /app
 
 COPY --from=builder /app/app/index_local.html app/index.html