use alpine's coreutils base64, which supports -w 0 to avoid wrapping -- thanks @miihael

Author: ricardop

Dockerfile

@@ -4,7 +4,7 @@ FROM rpardini/nginx-proxy-connect-stable-alpine:nginx-1.16.1-alpine-3.11
 
 # Add openssl, bash and ca-certificates, then clean apk cache -- yeah complain all you want.
 # Also added deps for mitmproxy.
-RUN apk add --update openssl bash ca-certificates su-exec git g++ libffi libffi-dev libstdc++ openssl openssl-dev python3 python3-dev \
+RUN apk add --update openssl bash ca-certificates su-exec coreutils git g++ libffi libffi-dev libstdc++ openssl openssl-dev python3 python3-dev \
  && LDFLAGS=-L/lib pip3 install mitmproxy \
  && apk del --purge git g++ libffi-dev openssl-dev python3-dev \
  && rm -rf /var/cache/apk/* \

entrypoint.sh

@@ -57,8 +57,7 @@ if [ "$AUTH_REGISTRIES" ]; then
         AUTH_HOST="${registry_array[0]}"
         AUTH_USER="${registry_array[1]}"
         AUTH_PASS="${registry_array[2]}"
-        # make base64 not wrap lines: https://superuser.com/a/1225334
-        AUTH_BASE64=$(echo -n "${AUTH_USER}:${AUTH_PASS}" | base64 | tr -d \\n )
+        AUTH_BASE64=$(echo -n ${AUTH_USER}:${AUTH_PASS} | base64 -w0 | xargs)
         echo "Adding Auth for registry '${AUTH_HOST}' with user '${AUTH_USER}'."
         echo "\"${AUTH_HOST}\" \"${AUTH_BASE64}\";" >> /etc/nginx/docker.auth.map
     done