Set correct platform type for arm v8 docker images

- A previous attempt used the wrong platform value which resulted in a build without the v8 variant being
created.
- Platform formatting is defined in the containerd source code as referenced by the docker documentation:
https://github.com/containerd/containerd/blob/v1.4.3/platforms/platforms.go#L63

Fixes #1593 - again

CHANGELOG.md

@@ -9,6 +9,7 @@
 ## Changes since v7.4.0
 
 - [#1882](https://github.com/oauth2-proxy/oauth2-proxy/pull/1882) Make `htpasswd.GetUsers` racecondition safe
+- [#1883](https://github.com/oauth2-proxy/oauth2-proxy/pull/1883) Ensure v8 manifest variant is set on docker images
 
 # V7.4.0
 

Dockerfile

@@ -35,7 +35,7 @@ RUN case ${TARGETPLATFORM} in \
          "linux/amd64")  GOARCH=amd64  ;; \
          # arm64 and arm64v8 are equivilant in go and do not require a goarm
          # https://github.com/golang/go/wiki/GoArm
-         "linux/arm64" | "linux/arm64/v8")  GOARCH=arm64  ;; \
+         "linux/arm64" | "linux/arm/v8")  GOARCH=arm64  ;; \
          "linux/ppc64le")  GOARCH=ppc64le  ;; \
          "linux/arm/v6") GOARCH=arm GOARM=6  ;; \
     esac && \

Makefile

@@ -39,7 +39,7 @@ build: validate-go-version clean $(BINARY)
 $(BINARY):
 	CGO_ENABLED=0 $(GO) build -a -installsuffix cgo -ldflags="-X main.VERSION=${VERSION}" -o $@ github.com/oauth2-proxy/oauth2-proxy/v7
 
-DOCKER_BUILD_PLATFORM ?= linux/amd64,linux/arm64,linux/ppc64le,linux/arm/v6,linux/arm64/v8
+DOCKER_BUILD_PLATFORM ?= linux/amd64,linux/ppc64le,linux/arm/v6,linux/arm/v8
 DOCKER_BUILD_RUNTIME_IMAGE ?= alpine:3.15
 DOCKER_BUILDX_ARGS ?= --build-arg RUNTIME_IMAGE=${DOCKER_BUILD_RUNTIME_IMAGE}
 DOCKER_BUILDX := docker buildx build ${DOCKER_BUILDX_ARGS} --build-arg VERSION=${VERSION}