Zowe CLI stores credentials in plain text. However, you don't need to always store your credentials in the CLI. Zowe CLI is able to accept credentials from other sources such as environment variables.

Using it from automation tools like Jenkins which has its own secure credential storage capability https://jenkins.io/doc/developer/security/secrets/ allows the CLI to consume secure credentials via environment variables.

In the case where you're using it from your laptop and you'd like to store your credentials securely, there are 3rd party plugins available for Zowe that accomplish this.

Thanks,