Follow steps 2 and 3 here to create an account on Sonatype: https://docs.sonatype.org/display/Repository/Sonatype+OSS+Maven+Repository+Usage+Guide
https://docs.sonatype.org/display/Repository/How+To+Generate+PGP+Signatures+With+Maven
If you don't have gpg
installed: brew install gpg
Create a key by running gpg --gen-key
and make sure to save your passphrase.