the quick way
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cd /etc/apt
sudo cp trusted.gpg trusted.gpg.d
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wget --quiet -O - https://www.example.com/some-gpg-key.gpg | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/<repository>-archive-keyring.gpg
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wget -O- <https://example.com/key/repo-key.gpg> | gpg --dearmor | sudo tee /usr/share/keyrings/<myrepository>-archive-keyring.gpg