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This is something I wrote for myself for an old project in 2024, lightly modified.
OpenID Connect
OpenID Connect (OIDC) is an open authentication protocol based on OAuth2 and allows the program to be made without having to implement the authentication details ourselves.
This page on how OpenID Connect works gives a very brief overview but not really enough to implement anything (for me). This guide aims to provide enough to be able to implement a client using OIDC, at least using an OIDC library. The sequence diagram below gives an idea of the flow of the code for the a server:
sequenceDiagram
participant O as OidcAndIdp
participant D as OurServer
participant U as User
D ->> U: Login URL
U ->> O: Login
O -->> D: Authorisation code
D ->> O: Key exchange request
O -->> D: Access tokenAuthenticating and Authorisation
This part of the document will follow a script obtains an OIDC token and refresh token. The script authenticates a user and retrieves an access token which can be used to retrieve information from the identity provider (IDP) The code shown in this document will have extra comments to explain what is going on in terms of OIDC flow.
The imports used in this code are:
use dotenvy::dotenv;
use openidconnect as oidc;
use openidconnect::OAuth2TokenResponse;
use std::{
io::{BufRead, BufReader, Write},
net::TcpListener,
};
use url::Url;Get Client and Authorisation URL
dotenv().ok();
let client = get_client().await.unwrap();
let (auth_url, csrf_state, _nonce) = get_auth_url(&client);
println!("Open this url: {auth_url}");The first line in this code loads environment variables that may be
specified in a .env file. The next line uses environment
variables to construct the client:
pub async fn get_client() -> Result<oidc::core::CoreClient, Box<dyn std::error::Error>> {
// Get client id from environment variables.
let client_id = oidc::ClientId::new(std::env::var("OIDC_CLIENT_ID")?);
// Discover the metadata by asking the OIDC provider so we don't have to
// specify ourselves.
let provider_metadata = oidc::core::CoreProviderMetadata::discover_async(
// Get the issuer URL from environment variable also.
// For a KeyCloak server it will be something like:
//
// https://<DOMAIN>:<PORT>:/realms/<REALM>
oidc::IssuerUrl::new(std::env::var("OIDC_ISSUER_URL")?)?,
oidc::reqwest::async_http_client,
)
.await?;
Ok(
// The final argument (None) is the client secret which we do not have as most of the time
// users will authenticate via the web interface, which does not allow to keep a secret.
oidc::core::CoreClient::from_provider_metadata(provider_metadata, client_id, None)
// Set the redirect URL to the URL that we will be listening on.
// In the case of this script, we will start a local HTTP server on port 8080.
//
// Make sure that the redirect URL is allowed in the OIDC provider settings.
.set_redirect_uri(oidc::RedirectUrl::new(
"http://localhost:8080/auth_cb".to_string(),
)?),
)
}The remaining lines get the authorisation URL and print it to the
terminal so that the user can open it in the browser to authenticate.
The code in get_auth_url is quite self explanatory:
pub fn get_auth_url(
client: &oidc::core::CoreClient,
) -> (reqwest::Url, oidc::CsrfToken, oidc::Nonce) {
client
.authorize_url(
oidc::AuthenticationFlow::<oidc::core::CoreResponseType>::AuthorizationCode,
oidc::CsrfToken::new_random,
oidc::Nonce::new_random,
)
.add_scope(oidc::Scope::new("email".to_string()))
.add_scope(oidc::Scope::new("profile".to_string()))
.url()
}Cross Site Request Forgery (CSRF)
Along with the authorisation URL, the function returns a cross site request forgery (for more: https://owasp.org/www-community/attacks/csrf) token and a nonce (which can be used to prevent replay attacks). These topics are out of the scope of this document and won’t be handled/used in this code.
Receiving Code to Exchange for Token
Once the user has been logged in and been redirected to back to our site, we will be able to get the authorisation code returned by the server by looking in the URL query parameters:
http://localhost:8080/auth_cb
?state=<CSRF_STATE>
&code=<AUTHORISATION_CODE>The state parameter is to be used for CSRF prevention (I
believe) and the code can be exchanged to receive a
token:
let token_response = client
.exchange_code(code)
.request_async(oidc::reqwest::async_http_client)
.await
.unwrap();
println!(
"Received access token: {}",
token_response.access_token().secret()
);
match token_response.expires_in() {
Some(expir) => println!("Access token expires in : {:?}", expir),
None => println!("No standard expiration given"),
};
// Technically a refresh token does not need to be issued, but a lot of this project will assume
// a refresh token will be issued.
// If it is not, then we need to redirect user to authorise/authenticate again once the access token
// expires.
match token_response.refresh_token() {
Some(token) => println!("Received refresh token: {}", token.secret()),
None => println!("No refresh token provided"),
};
Local Web Server to
Retrieve Access Code
The code used to host local web server for the redirect URL is not
very interesting but is included here for completeness (click to
show).
// Create a listener, and wait for one connection
let listener = TcpListener::bind("0.0.0.0:8080").unwrap();
let (mut stream, _) = listener.accept().unwrap();
let code;
let state;
{
// Reading and parsing the request into a Url object
let mut reader = BufReader::new(&stream);
let mut request_line = String::new();
reader.read_line(&mut request_line).unwrap();
let redirect_url = request_line.split_whitespace().nth(1).unwrap();
let url = Url::parse(&("http://localhost".to_string() + redirect_url)).unwrap();
// Finding the query parameters (code)
let code_pair = url
.query_pairs()
.find(|pair| {
let (key, _) = pair;
key == "code"
})
.unwrap();
let (_, value) = code_pair;
code = oidc::AuthorizationCode::new(value.into_owned());
// Finding the query parameters (state)
let state_pair = url
.query_pairs()
.find(|pair| {
let (key, _) = pair;
key == "state"
})
.unwrap();
let (_, value) = state_pair;
state = oidc::CsrfToken::new(value.into_owned());
}
// Send response back to user
let message = "Return to terminal";
let response = format!(
"HTTP/1.1 200 OK\r\ncontent-length: {}\r\n\r\n{}",
message.len(),
message
);
stream.write_all(response.as_bytes()).unwrap();Getting User Claims/Authenticating with Token
Now that we have the access token we can retrieve user information from the server. For our project that isn’t very interesting, but since our IDP will check the access token, an authorised response means that our access token is valid and is authenticated. This is the model for authentication.
let claims: oidc::UserInfoClaims<oidc::EmptyAdditionalClaims, oidc::core::CoreGenderClaim> =
client
.user_info(token_response.access_token().clone(), None)
.unwrap()
.request_async(oidc::reqwest::async_http_client)
.await
.unwrap();
println!("Claims: {:?}", claims);page rendered by gronk