On the Websec.io site there's a new tutorial posted showing a potential method for keeping secrets safe in PHP-based applications.
One of the most difficult things in any kind of application (not just web applications) is how to protect "secret" values. These values might be API keys, database passwords or even special bypass codes. Ideally, you're not having to define these directly in the application and can have them loaded from another source.
While a lot of the issues around protecting secrets can be removed by better secret handling, it seems like there's still always a need for some kind of secret value to exist in an application. Using this sort of pattern is, obviously, recommended against. The Common Weakness Enumeration database even has an entry specifically about it: CWE-798. Hard-coding credentials, especially plain-text ones, can be a huge risk if an attacker were able to somehow access the code and read them directly.
The post then goes on to talk about specific issues with secrets/credentials handling in PHP and some of the common approaches (mostly using a
.env file). It covers some of the basics of using the phpdotenv package before getting into the encryption of the secrets it contains. It makes the recommendation of using an "Apache pull" method to pull in the encryption key when Apache starts, putting it into an environment variable and using the psecio/secure_dotenv library to work with the encrypted values.