Use caddy's certmagic library for extensible/robust ACME handling (#14177)

* use certmagic for more extensible/robust ACME cert handling

* accept TOS based on config option

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lauris BH <lauris@nix.lv>

vendor/go.uber.org/atomic/Makefile

@@ -0,0 +1,35 @@
+# Directory to place `go install`ed binaries into.
+export GOBIN ?= $(shell pwd)/bin
+
+GOLINT = $(GOBIN)/golint
+
+GO_FILES ?= *.go
+
+.PHONY: build
+build:
+	go build ./...
+
+.PHONY: test
+test:
+	go test -race ./...
+
+.PHONY: gofmt
+gofmt:
+	$(eval FMT_LOG := $(shell mktemp -t gofmt.XXXXX))
+	gofmt -e -s -l $(GO_FILES) > $(FMT_LOG) || true
+	@[ ! -s "$(FMT_LOG)" ] || (echo "gofmt failed:" && cat $(FMT_LOG) && false)
+
+$(GOLINT):
+	go install golang.org/x/lint/golint
+
+.PHONY: golint
+golint: $(GOLINT)
+	$(GOLINT) ./...
+
+.PHONY: lint
+lint: gofmt golint
+
+.PHONY: cover
+cover:
+	go test -coverprofile=cover.out -coverpkg ./... -v ./...
+	go tool cover -html=cover.out -o cover.html