authentic

A Rust crate to handle authentication of HTTP calls. Documentation at https://docs.rs/authentic/latest/authentic/.

Authentication schemes can require specific workflows, such as making third-party calls to refresh a token or performing an initial request to get challenge information.

Using a fixed code structure, authentic can perform the necessary interactions for each authentication scheme. This allows schemes to be changed easily.

For example, the following code uses reqwest to access a site using HTTP Basic authentication. (See the repository tests directory for fully working examples).

let client = ::reqwest::Client::new();

let credential = UsernamePasswordCredential::new("username".into(), "password".into());
let mut scheme = HttpAuthentication::new(&credential).into_scheme();

let response = loop {
    while let Some(auth_step) = scheme.step() {
        match auth_step {
            AuthenticationStep::Request(request) => {
                let auth_response = client.execute(request).await;
                scheme.respond(auth_response);
            }
            AuthenticationStep::WaitFor(duration) => {
                time::sleep(duration).await;
            }
        }
    }
    let request = client
        .get("https://httpbin.org/basic-auth/username/password")
        .with_authentication(&scheme)
        .build()?;

    let response = client.execute(request).await?;

    if scheme.has_completed(&response) {
        break response;
    }
};

The creation of the request takes place inside a loop. First, the authentication scheme is given an opportunity to perform any third-party calls using step(). HTTP Basic authentication does not use this, but it can be used, for example, to refresh an expired OAuth2 access token.

The request is created using a standard reqwest::RequestBuilder, using a new with_authentication() method to modify the request for the authentication scheme. For HTTP authentication, the first iteration makes no change to the request.

The request is sent and a response is received. For HTTP authentication, this returns a 401 Unauthorized response.

The has_completed() method checks if the response is ready to be returned or if the authentication scheme needs to retry. For HTTP authentication, this reads the returned www-authenticate challenge and updates the scheme to send the correct credentials. As the request needs to be retried, has_completed() returns false and a second iteration begins.

On the second iteration of the loop, with_authentication() adds the credentials as the Authorization header to the request. The request is authenticated and the response contains the correct data. has_completed() will return true and the loop exits with the response.