How do I add a CA root certificate inside a docker image?

I am running an ASP.NET Core 1.1 Web API in a Docker 1.13.1 container on Ubuntu 14.04.

When the code attempts to retrieve some data from an HTTPS server, I get this certificate authentication error:

 An error occurred while sending the request. ---> System.Net.Http.CurlException: Peer certificate cannot be authenticated with given CA certificates
   at System.Net.Http.CurlHandler.ThrowIfCURLEError(CURLcode error)
   at System.Net.Http.CurlHandler.MultiAgent.FinishRequest(StrongToWeakReference`1 easyWrapper, CURLcode messageResult)

The HTTPS server is internal with certificate signed by our corporate CA, so am aware that I may need to register the internal CA.

Everything I've found so far about this error and Docker talks to getting docker itself running, connecting to repos etc. My Docker is working fine, and the Web API runs on the Ubuntu server outside of the container without a problem.

1. Do I need to add a CA root certificate inside a docker image?

2. If so, how do I do it?

3. If not, how do I fix this?

The task itself is not specific to docker as you would need to add that CA on a normal system too. There is an answer on the askubuntu community on how to do this.

So in a Dockerfile you would do the following (don't forget chmod in case you're running the container with a user other than root):

ADD your_ca_root.crt /usr/local/share/ca-certificates/foo.crt
RUN chmod 644 /usr/local/share/ca-certificates/foo.crt && update-ca-certificates

To simplify/standardise all container builds, we now host our certificates on a central HTTPS server and build them into our containers like this:

# Debian stretch based container
RUN curl -ks 'https://cert.host.server/ssl_certs/EnterpriseRootCA.crt' -o '/usr/local/share/ca-certificates/EnterpriseRootCA.crt'
RUN /usr/sbin/update-ca-certificates

Alpine-based containers don't have the tools immediately available so require a bit more work to achieve the same:

# Alpine based containers
RUN apk update && apk add curl
WORKDIR /usr/local/share/ca-certificates
RUN curl -ks 'https://cert.host.server/ssl_certs/EnterpriseRootCA.crt' -o '/usr/local/share/ca-certificates/EnterpriseRootCA.crt'
RUN /usr/sbin/update-ca-certificates

If you also want to update your Java truststore (same as on any computer):

RUN keytool -keystore /usr/lib/jvm/java-8-oracle/jre/lib/security/cacerts -storepass changeit -noprompt -trustcacerts -importcert -alias EnterpriseRootCA -file EnterpriseRootCA.crt

It's also worth noting that this definitely needs to use the .crt extension. I initially tried this with a .pem cert file (I thought they were interchangeable, so others might also), which is not linked by update-ca-certificates.

Installing ca-certificates locate cert_file_name.crt file in the same directory as Dockerfile.

# Install ca-certificates
# Please locate cert_file_name.crt file in the same directory as Dockerfile.
COPY cert_file_name.crt /usr/share/ca-certificates/
RUN echo cert_file_name.crt >> /etc/ca-certificates.conf
RUN update-ca-certificates

This will update certificates in the Dockerfile.

Another option is to use OpenSSL. Replace domain_name with the URL you can retrieve the CA

RUN openssl s_client -connect <domain_name>:443 -showcerts </dev/null 2>/dev/null | sed -e '/-----BEGIN/,/-----END/!d' | tee "/usr/local/share/ca-certificates/ca.crt" >/dev/null && \
update-ca-certificates