Error `x509: certificate signed by unknown authority` when `docker login`

Issue

• When you login using docker login to docker-registry exposed externally from client host installed docker, it shows the following a error message.

# docker login -u admin -p aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa docker-registry-default.app.example.com
Error response from daemon: Get https://docker-registry-default.app.example.com/v1/users/: x509: certificate signed by unknown authority