Dotnet restore in docker build with private Azure artifacts feed(dotnet sdk >2.1.500 )

Dockerfile

# downloading the dotnet sdk image. Could be any docker sdk image with sdk > 2.1.500
FROM microsoft/dotnet:2.1-sdk AS dotnet-builder
ARG FEED_URL
ARG PAT

# download and install latest credential provider. Not required after https://github.com/dotnet/dotnet-docker/issues/878
RUN wget -qO- https://raw.githubusercontent.com/Microsoft/artifacts-credprovider/master/helpers/installcredprovider.sh | bash

#Optional
WORKDIR /workdir
COPY ./ .

# Environment variable to enable seesion token cache. More on this here: https://github.com/Microsoft/artifacts-credprovider#help
ENV NUGET_CREDENTIALPROVIDER_SESSIONTOKENCACHE_ENABLED true

# Environment variable for adding endpoint credentials. More on this here: https://github.com/Microsoft/artifacts-credprovider#help
# Add "FEED_URL" AND "PAT" using --build-arg in docker build step. "endpointCredentials" field is an array, you can add multiple endpoint configurations.
# Make sure that you *do not* hard code the "PAT" here. That is a sensitive information and must not be checked in.
ENV VSS_NUGET_EXTERNAL_FEED_ENDPOINTS {\"endpointCredentials\": [{\"endpoint\":\"${FEED_URL}\", \"username\":\"ArtifactsDocker\", \"password\":\"${PAT}\"}]}

# Use this if you have a nuget.config file with all the endpoints.
RUN dotnet restore

# Optional: Extended step to build the app using dotnet msbuild. 
RUN dotnet build dirs.proj