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/multierr/Makefile

@@ -0,0 +1,42 @@
+# Directory to put `go install`ed binaries in.
+export GOBIN ?= $(shell pwd)/bin
+
+GO_FILES := $(shell \
+	find . '(' -path '*/.*' -o -path './vendor' ')' -prune \
+	-o -name '*.go' -print | cut -b3-)
+
+.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 - $(FMT_LOG) && false)
+
+.PHONY: golint
+golint:
+	@go install golang.org/x/lint/golint
+	@$(GOBIN)/golint ./...
+
+.PHONY: staticcheck
+staticcheck:
+	@go install honnef.co/go/tools/cmd/staticcheck
+	@$(GOBIN)/staticcheck ./...
+
+.PHONY: lint
+lint: gofmt golint staticcheck
+
+.PHONY: cover
+cover:
+	go test -coverprofile=cover.out -coverpkg=./... -v ./...
+	go tool cover -html=cover.out -o cover.html
+
+update-license:
+	@go install go.uber.org/tools/update-license
+	@$(GOBIN)/update-license $(GO_FILES)