How do I avoid a "x509: certificate signed by unknown authority" when doing a "go get download" from an alpine container?

I am trying to build coredns from scratch with the following Dockerfile:

FROM golang:alpine
SHELL [ "/bin/sh", "-ec" ]

RUN apk update && apk add --no-cache git make ca-certificates openssl && update-ca-certificates
RUN  git clone https://github.com/coredns/coredns.git
WORKDIR /go/coredns
RUN go get download
RUN make

When I run docker build --no-cache --progress=plain -t coredns . this is the output and error I am getting:

#1 [internal] load build definition from Dockerfile
#1 sha256:5b65661f68f3298655d88d1e83c5014118e9d278e724f83e2f8d968a8f11fe27
#1 transferring dockerfile: 619B done
#1 DONE 0.0s

#2 [internal] load .dockerignore
#2 sha256:2e78fdc563f1836b7815b48a445b2878de57404b5573a93080990b3c49e92f8f
#2 transferring context: 2B done
#2 DONE 0.0s

#3 [internal] load metadata for docker.io/library/golang:alpine
#3 sha256:299327d28eff710219f2e24597cfa9b226e8b1b0dc90f9e2122573004cfe837f
#3 DONE 0.5s

#4 [1/6] FROM docker.io/library/golang:alpine@sha256:2381c1e5f8350a901597d633b2e517775eeac7a6682be39225a93b22cfd0f8bb
#4 sha256:bcd1e622e133c928bad4175797b9e323eb9ac29a1d90fbb12f2566da7e868b8f
#4 CACHED

#5 [2/6] RUN apk update && apk add --no-cache git make ca-certificates openssl && update-ca-certificates
#5 sha256:6dd058a5b7f80d591599c7ab466c65cf38e8d5d1b7ddb8f4d2e5d1c0e79a32f0
#5 0.198 fetch https://dl-cdn.alpinelinux.org/alpine/v3.17/main/x86_64/APKINDEX.tar.gz
#5 0.847 fetch https://dl-cdn.alpinelinux.org/alpine/v3.17/community/x86_64/APKINDEX.tar.gz
#5 1.224 v3.17.1-21-gf40c2ce77f [https://dl-cdn.alpinelinux.org/alpine/v3.17/main]
#5 1.224 v3.17.1-23-g06668be47f [https://dl-cdn.alpinelinux.org/alpine/v3.17/community]
#5 1.224 OK: 17813 distinct packages available
#5 1.280 fetch https://dl-cdn.alpinelinux.org/alpine/v3.17/main/x86_64/APKINDEX.tar.gz
#5 1.753 fetch https://dl-cdn.alpinelinux.org/alpine/v3.17/community/x86_64/APKINDEX.tar.gz
#5 2.043 (1/8) Installing brotli-libs (1.0.9-r9)
#5 2.120 (2/8) Installing nghttp2-libs (1.51.0-r0)
#5 2.182 (3/8) Installing libcurl (7.87.0-r1)
#5 2.257 (4/8) Installing libexpat (2.5.0-r0)
#5 2.314 (5/8) Installing pcre2 (10.42-r0)
#5 2.387 (6/8) Installing git (2.38.2-r0)
#5 2.622 (7/8) Installing make (4.3-r1)
#5 2.686 (8/8) Installing openssl (3.0.7-r2)
#5 2.763 Executing busybox-1.35.0-r29.trigger
#5 2.774 OK: 17 MiB in 24 packages
#5 DONE 2.9s

#6 [3/6] RUN  git clone https://github.com/coredns/coredns.git
#6 sha256:aae1eab60ab1f0ffb8d8a48bd03ef02b93bb537b82f1bd4285cfcb2731e19ff4
#6 0.264 Cloning into 'coredns'...
#6 DONE 14.1s

#7 [4/6] WORKDIR /go/coredns
#7 sha256:2291c568fa24f46c6531c6e7d41d5e1150d10485b34e88a85f81542e26295acb
#7 DONE 0.0s

#8 [5/6] RUN go get download
#8 sha256:b2878fe66127be7ffe2e7f4e1f6b538679aebda0abffdd20b14bf928ef23957f
#8 3.603 go: cloud.google.com/go/compute@v1.14.0: Get "https://proxy.golang.org/cloud.google.com/go/compute/@v/v1.14.0.mod": x509: certificate signed by unknown authority
#8 ERROR: executor failed running [/bin/sh -ec go get download]: exit code: 1
------
 > [5/6] RUN go get download:
------
executor failed running [/bin/sh -ec go get download]: exit code: 1

I've googled my heart out trying to figure out how to get past the "x509: certificate signed by unknown authority" error. Any help is appreciated.

It looks like the issue was caused by the Cisco AnyConnect client on my Mac. You can uninstall Cisco AnyConect or add the following to your Dockerfile.

RUN wget http://www.cisco.com/security/pki/certs/ciscoumbrellaroot.cer
RUN openssl x509 -inform DER -in ciscoumbrellaroot.cer -out ciscoumbrellaroot.crt
RUN cp ciscoumbrellaroot.crt /usr/local/share/ca-certificates/ciscoumbrellaroot.crt
RUN update-ca-certificates

I found the answer here.