Harshicorp Vault
Harshicorp Vault is a solution to secure store and get sensitive information. It has a lot of features, like One Time Password, many auth methods, policies, temp tokens, etc.
For this solution will be used a basic auth with token (no refreshment) to query vault, simple Key/Value will store keys/passwords. Of course it can and should be improved, like using policies, temp tokens, other auth methods, lease duration, etc. You can (and should) also limit requests for secrets based on IP addresses.