feat: support client verify for derp (add integration tests) (#2046)

* feat: support client verify for derp

* docs: fix doc for integration test

* tests: add integration test for DERP verify endpoint

* tests: use `tailcfg.DERPMap` instead of `[]byte`

* refactor: introduce func `ContainsNodeKey`

* tests(dsic): use string builder for cmd args

* ci: fix tests order

* tests: fix derper failure

* chore: cleanup

* tests(verify-client): perfer to use `CreateHeadscaleEnv`

* refactor(verify-client): simplify error handling

* tests: fix `TestDERPVerifyEndpoint`

* refactor: make `doVerify` a seperated func

---------

Co-authored-by: 117503445 <t117503445@gmail.com>

Dockerfile.derper

@@ -0,0 +1,19 @@
+# For testing purposes only
+
+FROM golang:alpine AS build-env
+
+WORKDIR /go/src
+
+RUN apk add --no-cache git
+ARG VERSION_BRANCH=main
+RUN git clone https://github.com/tailscale/tailscale.git --branch=$VERSION_BRANCH --depth=1
+WORKDIR /go/src/tailscale
+
+ARG TARGETARCH
+RUN GOARCH=$TARGETARCH go install -v ./cmd/derper
+
+FROM alpine:3.18
+RUN apk add --no-cache ca-certificates iptables iproute2 ip6tables curl
+
+COPY --from=build-env /go/bin/* /usr/local/bin/
+ENTRYPOINT [ "/usr/local/bin/derper" ]