This question is generally similar to past questions asked here, but I haven't seen one the relates to Linux.
Case at hand: a PHP web app has a MySQL backend. As part of its functionality it accesses other, remote MySQL hosts and issues some queries on those hosts.
To allow that, the PHP app needs credentials for those remote databases. What is a reasonable way for it to store/fetch such credentials?
It is required that the users of the app do not provide such credentials themselves. Also, there could be dozens of users to this app.
All users of the app are identified via LDAP. The app and the entire set of MySQL servers lie within the same internal network (requires two step VPN verification). The entire setup runs on Linux machines.
What are reasonable solutions to this problem?