In order to configure the secret "azureregistrykey", run the following command. Running this on Ubuntu 18.04, I was unable to authentication using other methods.
kubectl create secret docker-registry azureregistrykey \
--docker-server=<your registry>.azurecr.io --docker-username=<your username> \
--docker-password=<your password> --docker-email=<youremail address>
Then ensure that imagePullSecrets matches "azureregistrykey" or whatever you've called it.