update variables

devops/Dockerfile

@@ -2,9 +2,9 @@ FROM mcr.microsoft.com/azure-cli
 
 LABEL maintainer="Microsoft Corporation"
 
-RUN az login --service-principal -u [AZURE_CLIENT_ID] -p=[AZURE_CLIENT_SECRET] --tenant [AZURE_TENANT_ID] && \
-az account set -s [AZURE_SUBSCRIPTION_ID] && \
-az aks get-credentials -n [CLUSTERNAME] -g [RESOURCEGROUP] --admin
+RUN az login --service-principal -u "${AZURE_CLIENT_ID}" -p="${AZURE_CLIENT_SECRET}" --tenant "${AZURE_TENANT_ID}" && \
+az account set -s "${AZURE_SUBSCRIPTION_ID}" && \
+az aks get-credentials -n "${CLUSTERNAME}" -g "${RESOURCEGROUP}" --admin
 
 WORKDIR /