I have very little experience with GCP and Azure, but it seems like Hashicorp is reinventing the wheel in AWS with Vault.
You can also specify vault-password-file in ansible.cfg [1] It can be a shell script rather than plaintext, so you can use it to call the CLI password manager "pass"[2] for instance. This is handy for automation.
[1] http://docs.ansible.com/ansible/latest/intro_configuration.h... [2] https://www.passwordstore.org/
Oddly enough though, I recently tried AWX (the open sourced Ansible Tower), and it wouldn't decrypt our vaults when trying to get the inventory, even though I gave it vault credentials (there was nowhere to associate it with the inventory run though).
So, we are still using RunDeck for a web UI/scheduling/web triggers/Slack integration of our Ansible runs.
I think a large part of our problem is that we are using Ganeti for most of our VMs, rather than something supported native by AWX like OpenStack/EC2/Azure. I have an inventory script we have been using, but couldn't get it to run in AWX due to AWS credentials not being made available in a way that boto recognized (the inventory is pulled both from Ganeti and EC2).
https://docs.ansible.com/ansible/latest/playbooks_vault.html