[Solved] gpgkeys: protocol `https' not supported

Problem:

sudo apt-key adv --fetch-keys 'https://mariadb.org/mariadb_release_signing_key.asc'
Executing: /tmp/tmp.o2I4wt3O3r/gpg.1.sh --fetch-keys
https://mariadb.org/mariadb_release_signing_key.asc
gpgkeys: protocol `https' not supported
gpg: no handler for keyserver scheme `https'
gpg: WARNING: unable to fetch URI https://mariadb.org/mariadb_release_signing_key.asc: keyserver error

Method 1: Install gnupg-curl

apt-get update
apt-get install gnupg-curl

Method 2: If the above does not resolve the issue, then get the key using CURL and add it manually

curl 'https://mariadb.org/mariadb_release_signing_key.asc' | apt-key add -

Method 3: If you trust the server, then use -k option to skip CA cert verification

curl -k 'https://mariadb.org/mariadb_release_signing_key.asc' | apt-key add -

The method 2 worked for me on Ubuntu Xenial.

Comment if it helped you or if you are aware of a better solution.

Thanks.