Adding architecture support for arm/arm64/amd64 docker images (#1781)

add multi-arch image support for armv7/arm64/amd64 architectures

Dockerfile

@@ -1,11 +1,25 @@
 FROM golang:1.14-alpine
 
+ARG TARGETOS
+ARG TARGETARCH
+ARG TARGETVARIANT=""
+
+WORKDIR /go/src/github.com/dexidp/dex
+
+ENV GOOS=${TARGETOS} \
+  GOARCH=${TARGETARCH} \
+  GOARM=${TARGETVARIANT}
+
 RUN apk add --no-cache --update alpine-sdk
 
-COPY . /go/src/github.com/dexidp/dex
-RUN cd /go/src/github.com/dexidp/dex && make release-binary
+COPY . .
+
+RUN make release-binary
 
 FROM alpine:3.12
+
+WORKDIR /
+
 # Dex connectors, such as GitHub and Google logins require root certificates.
 # Proper installations should manage those certificates, but it's a bad user
 # experience when this doesn't work out of the box.
@@ -14,12 +28,12 @@ FROM alpine:3.12
 RUN apk add --update ca-certificates openssl
 
 USER 1001:1001
+
 COPY --from=0 /go/bin/dex /usr/local/bin/dex
 
 # Import frontend assets and set the correct CWD directory so the assets
 # are in the default path.
-COPY web /web
-WORKDIR /
+COPY web .
 
 ENTRYPOINT ["dex"]