l402_middleware

A middleware library for rust that uses L402, formerly known as LSAT (a protocol standard for authentication and paid APIs) and provides handler functions to accept microtransactions before serving ad-free content or any paid APIs. It supports Lightning Network Daemon (LND), Lightning Node Connect (LNC), Core Lightning (CLN), Eclair, Lightning URL (LNURL), Nostr Wallet Connect (NWC), and BOLT12 for generating invoices.

Check out the Go version here: https://github.com/getAlby/lsat-middleware

The middleware:-

1. Checks the preference of the user whether they need paid content or free content.
2. Verify the L402 before serving paid content.
3. Send macaroon and invoice if the user prefers paid content and fails to present a valid L402.

It also supports location-scoped ("realm") tokens via caveats::RequestBinding — one payment can authorize a whole route rather than a single path — and server-side settlement detection via LNClient::lookup_invoice, so clients that can't return a usable preimage still work.

Settlement lookup is available on LND, CLN, BOLT12, and Eclair, and on NWC where the wallet implements the optional NIP-47 lookup_invoice. LNURL and LND over the LNC mailbox have no way to ask, and return an error. Settlement is always taken from the node's own status: a wallet knows the preimage of an invoice it minted before anyone pays it, so the preimage alone never counts as proof.

L402 Header Specifications

Caveats: what a token is bound to

A macaroon carries caveats that limit where it can be spent. The crate understands four:

RequestPath and Realm are alternatives — a token carries one or the other, never both. Build them with caveats::RequestBinding rather than by hand, so minting and verification cannot drift apart:

use l402_middleware::caveats::RequestBinding;

// Exact path — one payment buys one URL. The default.
let binding = RequestBinding::path(req.uri().path().to_string(), "GET");

// Realm — one payment buys every route naming "library".
let binding = RequestBinding::realm("library", "GET");

// Either can expire.
let binding = binding.with_expiry(Some(expires_at_unix_seconds));

let caveats = binding.to_caveats();   // mint these into the macaroon

Verify with the same binding:

use l402_middleware::l402;

l402::verify_l402_binding(&mac, &binding, root_key, preimage)?;

Bind the method. A binding always carries RequestMethod, so a token bought for GET will not satisfy a POST. Hand-rolled caveat lists frequently omit this, and a token that ignores the method is a token that can be replayed against a different handler on the same path.

Use verify_l402_binding where scope matters. The older verify_l402 exact-matches whatever caveat strings you hand it. It cannot evaluate ExpiresAt — it compares the string, so an expired token still matches — and it has no notion of realms. verify_l402_binding enforces scope and method by exact match, checks expiry against the clock, and rejects any scope or method predicate it was not given rather than letting it pass.

That last part is the security-critical one: a verifier that lets an unknown RequestPath or Realm predicate fall through to "satisfied" will accept a token minted for a different route. RequestBinding::verifier is the single place that guard lives, and the bypass tests at the bottom of caveats.rs cover it.

Installation

Add the crate to your Cargo.toml:

[dependencies]
l402_middleware = "2.3.3"

By using the no-accept-authenticate-required feature, the check for the Accept-Authenticate header can be bypassed, allowing L402 to be treated as the default authentication option.

[dependencies]
l402_middleware = { version = "2.3.3", features = ["no-accept-authenticate-required"] }

The Rocket integration (Fairing, request guards, demo server) is behind the rocket feature, which is on by default. Library consumers that only call the handler functions (e.g. ngx_l402) can disable default features to drop rocket from their dependency tree:

[dependencies]
l402_middleware = { version = "2.4.0", default-features = false }

Note: the rocket feature gate is not in a published release yet — 2.3.3 on crates.io predates it, so on 2.3.3 default-features = false is a no-op and rocket stays in the tree. This applies from the next published version.

Ensure that you create a .env file based on the provided .env_example and configure all the necessary environment variables.

Example

#[macro_use] extern crate rocket;

use rocket::serde::json::Json;
use rocket::serde::Serialize;
use rocket::http::Status;
use rocket::Request;
use dotenv::dotenv;
use std::env;
use std::sync::Arc;
use reqwest::Client;

use l402_middleware::{l402, lnclient, lnd, lnurl, nwc, cln, bolt12, eclair, middleware};
use l402_middleware::caveats::RequestBinding;

const SATS_PER_BTC: i64 = 100_000_000;
const MIN_SATS_TO_BE_PAID: i64 = 1;
const MSAT_PER_SAT: i64 = 1000;

#[derive(Serialize)]
#[serde(crate = "rocket::serde")]

pub struct FiatRateConfig {
    pub currency: String,
    pub amount: f64,
}

impl FiatRateConfig {
     // Converts fiat amount to BTC equivalent in millisats. Customization possible for different API endpoints.
    pub async fn fiat_to_btc_amount_func(&self) -> i64 {
        // Return the minimum sats if the amount is invalid.
        if self.amount <= 0.0 {
            return MIN_SATS_TO_BE_PAID * MSAT_PER_SAT;
        }

        // API request to get BTC equivalent of the fiat amount.
        let url = format!(
            "https://blockchain.info/tobtc?currency={}&value={}",
            self.currency, self.amount
        );

        match Client::new().get(&url).send().await {
            Ok(res) => {
                let body = res.text().await.unwrap_or_else(|_| MIN_SATS_TO_BE_PAID.to_string());
                match body.parse::<f64>() {
                    Ok(amount_in_btc) => ((SATS_PER_BTC as f64 * amount_in_btc) * MSAT_PER_SAT as f64) as i64,
                    Err(_) => MIN_SATS_TO_BE_PAID * MSAT_PER_SAT,
                }
            }
            Err(_) => MIN_SATS_TO_BE_PAID * MSAT_PER_SAT,
        }
    }
}

// Caveats the macaroon will carry. Customize as authentication needs require —
// but build them with RequestBinding, which also binds the HTTP method so a
// token bought for GET cannot be replayed against POST on the same path.
fn path_caveat(req: &Request<'_>) -> Vec<String> {
    RequestBinding::path(req.uri().path().to_string(), req.method().as_str())
        .to_caveats()
}

#[derive(Serialize)]
#[serde(crate = "rocket::serde")]

struct Response {
    code: u16,
    message: String
}

#[get("/")]
fn free() -> (Status, Json<Response>) {
    let response = Response {
        code: Status::Ok.code,
        message: String::from("Free content"),
    };

    (Status::Ok, Json(response))
}

#[get("/protected")]
fn protected(l402_info: l402::L402Info) -> (Status, Json<Response>) {
    let (status, message) = match l402_info.l402_type.as_str() {
        l402::L402_TYPE_FREE => (Status::Ok, String::from("Free content")),
        l402::L402_TYPE_PAYMENT_REQUIRED => (Status::PaymentRequired, String::from("Pay the invoice attached in response header")),
        l402::L402_TYPE_PAID => (Status::Ok, String::from("Protected content")),
        l402::L402_TYPE_ERROR => (
            Status::InternalServerError,
            l402_info.error.clone().unwrap_or_else(|| String::from("An error occurred")),
        ),
        _ => (Status::InternalServerError, String::from("Unknown type")),
    };

    let response = Response {
        code: status.code,
        message,
    };

    (status, Json(response))
}

#[launch]
pub async fn rocket() -> rocket::Rocket<rocket::Build> {
     // Load environment variables from .env file
    dotenv().ok();

    // Get LN_CLIENT_TYPE from the environment
    let ln_client_type = env::var("LN_CLIENT_TYPE").expect("LN_CLIENT_TYPE not found in .env");

    // Initialize LNClientConfig based on LN_CLIENT_TYPE
    let ln_client_config = match ln_client_type.as_str() {
        "LNURL" => lnclient::LNClientConfig {
            ln_client_type,
            lnd_config: None,
            lnurl_config: Some(lnurl::LNURLOptions {
                address: env::var("LNURL_ADDRESS").expect("LNURL_ADDRESS not found in .env"),
            }),
            nwc_config: None,
            cln_config: None,
            bolt12_config: None,
            eclair_config: None,
            root_key: env::var("ROOT_KEY")
                .expect("ROOT_KEY not found in .env")
                .as_bytes()
                .to_vec(),
        },
        "LND" => {
            // Check if using LNC
            let lnc_pairing_phrase = env::var("LNC_PAIRING_PHRASE").ok();
            let lnc_mailbox_server = env::var("LNC_MAILBOX_SERVER").ok();
            
            // Configure based on connection type
            let lnd_options = if lnc_pairing_phrase.is_some() {
                // LNC mode - only pairing phrase needed, no cert/macaroon required
                lnd::LNDOptions {
                    address: None,
                    macaroon_file: None,
                    cert_file: None,
                    socks5_proxy: None,
                    lnc_pairing_phrase,
                    lnc_mailbox_server,
                }
            } else {
                // Traditional mode - all required
                lnd::LNDOptions {
                    address: Some(env::var("LND_ADDRESS").expect("LND_ADDRESS not found in .env")),
                    macaroon_file: Some(env::var("MACAROON_FILE_PATH").expect("MACAROON_FILE_PATH not found in .env")),
                    cert_file: Some(env::var("CERT_FILE_PATH").expect("CERT_FILE_PATH not found in .env")),
                    socks5_proxy: env::var("SOCKS5_PROXY").ok(), // Optional: e.g., "127.0.0.1:9050" for Tor
                    lnc_pairing_phrase: None,
                    lnc_mailbox_server: None,
                }
            };
            
            lnclient::LNClientConfig {
                ln_client_type,
                lnd_config: Some(lnd_options),
                lnurl_config: None,
                nwc_config: None,
                cln_config: None,
                bolt12_config: None,
                eclair_config: None,
                root_key: env::var("ROOT_KEY")
                    .expect("ROOT_KEY not found in .env")
                    .as_bytes()
                    .to_vec(),
            }
        },
        "NWC" => lnclient::LNClientConfig {
            ln_client_type,
            lnd_config: None,
            lnurl_config: None,
            cln_config: None,
            bolt12_config: None,
            eclair_config: None,
            nwc_config: Some(nwc::NWCOptions {
                uri: env::var("NWC_URI").expect("NWC_URI not found in .env"),
            }),
            root_key: env::var("ROOT_KEY")
                .expect("ROOT_KEY not found in .env")
                .as_bytes()
                .to_vec(),
        },
        "CLN" => lnclient::LNClientConfig {
            ln_client_type,
            lnd_config: None,
            lnurl_config: None,
            nwc_config: None,
            bolt12_config: None,
            eclair_config: None,
            cln_config: Some(cln::CLNOptions {
                lightning_dir: env::var("CLN_LIGHTNING_RPC_FILE_PATH").expect("CLN_LIGHTNING_RPC_FILE_PATH not found in .env"),
            }),
            root_key: env::var("ROOT_KEY")
                .expect("ROOT_KEY not found in .env")
                .as_bytes()
                .to_vec(),
        },
        "BOLT12" => lnclient::LNClientConfig {
            ln_client_type,
            lnd_config: None,
            lnurl_config: None,
            nwc_config: None,
            cln_config: None,
            eclair_config: None,
            bolt12_config: Some(bolt12::Bolt12Options {
                lightning_dir: env::var("CLN_LIGHTNING_RPC_FILE_PATH").expect("CLN_LIGHTNING_RPC_FILE_PATH not found in .env"),
                offer: env::var("BOLT12_LN_OFFER").expect("BOLT12_LN_OFFER not found in .env"),
            }),
            root_key: env::var("ROOT_KEY")
                .expect("ROOT_KEY not found in .env")
                .as_bytes()
                .to_vec(),
        },
        "ECLAIR" => lnclient::LNClientConfig {
            ln_client_type,
            lnd_config: None,
            lnurl_config: None,
            nwc_config: None,
            cln_config: None,
            bolt12_config: None,
            eclair_config: Some(eclair::EclairOptions {
                api_url: env::var("ECLAIR_API_URL").expect("ECLAIR_API_URL not found in .env"),
                password: env::var("ECLAIR_PASSWORD").expect("ECLAIR_PASSWORD not found in .env"),
            }),
            root_key: env::var("ROOT_KEY")
                .expect("ROOT_KEY not found in .env")
                .as_bytes()
                .to_vec(),
        },
        _ => panic!("Invalid LN_CLIENT_TYPE. Expected 'LNURL', 'LND', 'NWC', 'CLN', 'BOLT12', or 'ECLAIR'."),
    };

    // Initialize Fiat Rate Config
    let fiat_rate_config = Arc::new(FiatRateConfig {
        currency: "USD".to_string(),
        amount: 0.01,
    });

    let l402_middleware = middleware::L402Middleware::new_l402_middleware(
        ln_client_config.clone(),
        Arc::new(move |_req: &Request<'_>| {
            let fiat_rate_config = Arc::clone(&fiat_rate_config);
            Box::pin(async move {
                fiat_rate_config.fiat_to_btc_amount_func().await
            })
        }),
        Arc::new(move |req: &Request<'_>| {
            path_caveat(req)
        }),
    ).await.unwrap();

    rocket::build()
        .attach(l402_middleware)
        .mount("/", routes![free, protected])
}

Testing

Run tests with:

• cargo test --verbose for standard tests
• cargo test --verbose --features "no-accept-authenticate-required" to run tests with accept-authenticate header requirements disabled