There are fair number of open source alternatives that allow you to store secrets in the cloud:

    vault: https://github.com/hashicorp/vault
    blackbox: https://github.com/StackExchange/blackbox
    git-crypt: https://www.agwa.name/projects/git-crypt/
    Pass: http://www.zx2c4.com/projects/password-store/
    Transcrypt: https://github.com/elasticdog/transcrypt
    Keyringer: https://keyringer.pw/
    git-secret: https://github.com/sobolevn/git-secret