This is ONLY meant for developing/testing Vault integration, and all secrets will only be stored on memory.
brew install vault will only install the vault pre-built binary,
which doesn't include the Vault Web UI.
Alternatively, go to https://www.vaultproject.io/downloads/ and download the latest release for your platform and place it in /usr/local/bin
vault server -dev
You will find the 'Unseal Key` and 'Root Token' from the console output, and you can also browse the web UI via http://127.0.0.1:8200/ui