# omnium
A set of extensions for building web applications on axum.
**Unstable:** This crate is not ready for use. The author is building out these extensions to iterate on a proof of concept, and the surface may change frequently.
## Responses
The `api::responses` module provides a set of response conventions for axum handlers, implementing axum's `IntoResponse` trait for typical use cases.
A handler returns `JsonResult<T>`:
```rs
// ...
use omnium::api::{JsonResult, JsonResponse, JsonStatus};
async fn handler() -> JsonResult<JsonStatus> {
let result = try_do_or_err().await;
match result {
Ok => JsonResponse::of_status(StatusCode::ACCEPTED).into()
Err => JsonResponse::of_status(StatusCode::CONFLICT).into()
}
}
```
You can build responses using `JsonResponse<T>`, which implements `Into<JsonResult>`, as well as axum's `IntoResponse`.
For clarity, you can use the provided `respond!` macro instead of calling `.into()`.
A handler can return a JSON response for any serializable body, with a default `OK` status:
```rs
async fn handler() -> JsonResult<SomeBodyType> {
respond!(JsonResponse::of(body));
}
```
Another status code can be set on the response:
```rs
async fn handler() -> JsonResult<JsonStatus> {
respond!(JsonResponse::of(body).with_status(StatusCode::IM_A_TEAPOT));
}
```
A handler can return a simple `JsonStatus` status response, implicitly deriving the response body as appropriate for the status:
```rs
async fn handler() -> JsonResult<JsonStatus> {
respond!(JsonResponse::of_status(StatusCode::OK));
}
```
An additional detail message can be added to the `JsonStatus`:
```rs
async fn handler() -> JsonResult<JsonStatus> {
respond!(JsonResponse::of_status(StatusCode::OK).with_detail("Additional detail"));
}
```
## Errors
A status response can be returned on the `Err` arm of `JsonResult`, regardless of the happy path response type.
```rs
async fn handler() -> JsonResult<()> {
Err(JsonResponse::of_status(StatusCode::OK).with_detail("Additional detail"))
}
```
An arbitrary error propagated to the top of a handler is treated as an internal server error, and is rendered with an opaque `INTERNAL_SERVER_ERROR` response that masks any error details from the caller.
```rs
async fn handler() -> JsonResult<()> {
let success = try_do_or_err().await?;
// ...
}
```
Run your application with the `RUST_BACKTRACE=1` environment variable set for such an internal error to display a backtrace when logged.
Depending on whether you are in a function returning `anyhow::Result` or `JsonResult`, you can return errors using `anyhow::bail!` or `respond_err!`, respectively. In both cases, you can propagate an arbitrary error to be handled as an internal server error, or you can provide a `JsonResult` status response.
```rs
async fn handler() -> anyhow::Result<()> {
anyhow::bail!("Internal error!");
// ...
}
```
```rs
async fn handler() -> JsonResult<()> {
respond_err!("Internal error!");
// ...
}
```
## Authentication
The `security` module provides JWT-based authentication middleware, with utilities for a cookie-based credential exchange or the `authorization` header for browser-based or programmatic authentication.
Create a service secret:
```rs
let service_secret = create_service_secret();
```
Configure authentication middleware:
```rs
#[derive(Clone)]
struct AppAccount {}
struct AppState {
pub service_secret: ServiceSecret,
}
impl SessionManager<AppAccount> for Arc<AppState> {
async fn get_service_secret(&self) -> anyhow::Result<&ServiceSecret> {
// Return secret from application secret manager:
Ok(&self.service_secret)
}
async fn get_account(&self, _account_id: String) -> anyhow::Result<Option<AppAccount>> {
// Return account from application database:
Ok(Some(AppAccount {}))
}
fn extract_credential(&self, request: &Request, _cookies: &CookieJar) -> Option<Credential> {
// Extract credential from request:
Credential::from_authorization_header(&request)
}
}
```
Attach authentication middleware:
```rs
fn app(state: Arc<AppState>) -> Router {
Router::new()
.route("/api/account", get(|| async { "Hello, caller!" }))
.layer(from_fn_with_state(
state.clone(),
authenticate::<AppAccount, Arc<AppState>>,
))
.layer(from_fn_with_state(
state.clone(),
decorate::<AppAccount, Arc<AppState>>,
))
.with_state(state)
}
```
Note that the authentication middleware is attached in two parts: 1) decorating the authenticated account on the request, and 2) enforcing authentication for the request.
Create the account session:
```rs
create_session(
"some-account-id",
&EncodingKey::from_secret(state.service_secret.value.as_bytes()),
Duration::from_secs(60),
);
```
With `Credential::from_authorization_header`, a client may pass the session as the `authorization` header. With `Credential::from_cookie`, a client may pass the session as the `__Host-omn-sess` cookie. For a simple, user-facing web application, you can set the `__Host-omn-sess` cookie when the account signs in, in order to authenticate requests to the service running on the same origin. If the application shares a session across multiple services on different origins, it can expose the session for use by the client in the `authorization` header for programmatic, cross-origin requests. You can plug in your own handling for extracting credentials from requests with a custom `extract_credential` handler.
Requests from an unauthenticated caller will reject with a 401 response.
For an authenticated caller, the account object from `account_lookup` can be retrieved from request state to avoid redundant lookup in handlers:
```rs
pub async fn handler(
Extension(caller): Extension<AppAccount>,
) {
println!("Caller is: {}", caller);
}
```
Because a variety of data may need to be passed and verified between an application and its callers, `encode_claims` and `decode_claims` may also be used for other purposes other than authentication. Note that claims are signed but not encrypted.
In addition to claims-based utilities, this crate wraps `aes_gcm` to provide utilties `encrypt_string_aes256_gcm` and `decrypt_string_aes256_gcm`. A secret created by `create_service_secret` can also be used with these encryption utilities.