The `decrypt` filter can be used in Tera templates to decrypt a string
using `age`. This will allow the template context to contain encrypted
vaules that are only decrypted if they are actually used to render a
template.
I considered using the [age] crate to implement this filter, rather
than using the `age` command, but I decided against it for two reasons:
1. The way I intend for the `keys.txt` file to be populated is by
fetching the keys from *keyserv.pyrocufflink.blue*, which returns
an encrypted file that has to be decrypted with the `age` command
before it can be used. Since that means `age` will always be
available, it makes less sense to increase the size of the `tmpl`
binary with what is effectively duplicate code.
2. The Rust API for *age* is rather un-ergonomic, particularly with
respect to loading identites from a file. It's much easier to
[age]: https://crates.io/crates/age
Dustin