# `libpam-sys-consts`: Constants for LibPAM

This crate does two primary things:

- Detects which implementation of LibPAM the current machine uses (as part of the build script), and exports that information to downstream crates.
- Exports the constants specific to that version of LibPAM.
  These are located in the `constants` module.

## Handling different PAM implmementations

Different PAM implementations have different constants and some different behaviors.
If you need to change your library's behavior based on PAM implementation, there are a few ways to do so.

### Constants

The current PAM implementation is available in `PamImpl::CURRENT`.
This is present as a string literal macro in `pam_impl_name!`.

### Conditional compilation

This package provides custom `#[cfg]`s to compile based on the current PAM implementation.

First, **enable custom `#[cfg]`s in your build.rs**:

```rust
// build.rs
use libpam_sys_helpers::pam_impl;

fn main() {
    pam_impl::enable_pam_impl_cfg();
    
    // everything else you do at build time
}
```

This will then allow you to use the `pam_impl` configuration variable at compile time:

```rust
#[cfg(pam_impl = "LinuxPam")]
fn handle_pam() {
    // do things in a Linux-PAM specific way
}

#[cfg(not(pam_impl = "LinuxPam"))]
fn handle_pam() {
    // do things in another, more different way
}
```

## Configuration

Known implementations of PAM are listed in the `PamImpl` enum, and your currently installed implementation is automatically detected.

If you need to configure this, you can override it **at build time** with the `LIBPAMSYS_IMPL` environment variable:

- Unset or `` (the default): Probe the currently installed LibPAM to figure out which implementation it is.
  If LibPAM is not present, this will fall back to `__TARGET_DEFAULT__`.
- `__TARGET_DEFAULT__`: Select the version of LibPAM most likely to be installed on the current OS.
  This is a useful setting for cross-compiling.
- The name of a `PamEnum` entry: The named PAM implementation.
  For instance, `LIBPAMSYS_IMPL=OpenPam cargo build` will build this library for OpenPAM.

## MSRV

This library supports **Rust 1.75**, as the version currently (July 2025) available in Debian Trixie and Ubuntu 24.04 LTS.