commit 0060778f15cc91b39e8ad98e499e484c28d52779
Author: Dirkjan Ochtman <dirkjan@instant.ca>
Date:   Tue Jan 25 15:06:38 2022 +0100

    rust: initial implementation of an ACME client

diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..1595204
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,13 @@
+[package]
+name = "acme"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+base64 = "0.13.0"
+reqwest = { version = "0.11", default-features = false, features = ["json", "rustls-tls-native-roots"] }
+ring = { version = "0.16.20", features = ["std"] }
+serde = { version = "1.0.104", features = ["derive"] }
+serde_json = "1.0.78"
+thiserror = "1.0.30"
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..78a0ecb
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,369 @@
+#![warn(unreachable_pub)]
+
+use std::sync::Arc;
+
+use base64::URL_SAFE_NO_PAD;
+use reqwest::header::{CONTENT_TYPE, LOCATION};
+use reqwest::redirect::Policy;
+use reqwest::{Body, Response};
+use ring::rand::SystemRandom;
+use ring::signature::{EcdsaKeyPair, ECDSA_P256_SHA256_FIXED_SIGNING};
+use serde::de::{DeserializeOwned, Error as _, Unexpected};
+use serde::{Deserialize, Serialize};
+
+mod types;
+use types::{
+    AccountCredentials, Challenge, DirectoryUrls, Empty, FinalizeRequest, Header, JoseJson, Jwk,
+    KeyAuthorization, KeyOrKeyId, OrderState, Problem, SigningAlgorithm,
+};
+pub use types::{
+    Authorization, ChallengeType, Error, Identifier, LetsEncrypt, NewAccount, NewOrder, OrderStatus,
+};
+
+pub struct Order {
+    account: Arc<AccountInner>,
+    nonce: Option<String>,
+    #[allow(dead_code)]
+    order_url: String,
+}
+
+impl Order {
+    pub async fn authorizations(
+        &mut self,
+        authz_urls: &[String],
+    ) -> Result<Vec<Authorization>, Error> {
+        let mut authorizations = Vec::with_capacity(authz_urls.len());
+        for url in authz_urls {
+            authorizations.push(self.account.get(&mut self.nonce, url).await?);
+        }
+        Ok(authorizations)
+    }
+
+    pub fn key_authorization(&self, challenge: &Challenge) -> KeyAuthorization {
+        KeyAuthorization(format!("{}.{}", challenge.token, &self.account.key.thumb))
+    }
+
+    pub async fn finalize(
+        &mut self,
+        csr_der: &[u8],
+        finalize_url: &str,
+    ) -> Result<OrderState, Error> {
+        let rsp = self
+            .account
+            .post(
+                Some(&FinalizeRequest::new(csr_der)),
+                self.nonce.take(),
+                finalize_url,
+            )
+            .await?;
+
+        self.nonce = nonce_from_response(&rsp);
+        Problem::check(rsp).await
+    }
+
+    pub async fn set_challenge_ready(&mut self, challenge_url: &str) -> Result<(), Error> {
+        let rsp = self
+            .account
+            .post(Some(&Empty {}), self.nonce.take(), challenge_url)
+            .await?;
+
+        self.nonce = nonce_from_response(&rsp);
+        let _ = Problem::check::<Challenge>(rsp).await?;
+        Ok(())
+    }
+
+    pub async fn certificate_chain(&mut self, cert_url: &str) -> Result<String, Error> {
+        let rsp = self
+            .account
+            .post(None::<&Empty>, self.nonce.take(), cert_url)
+            .await?;
+
+        self.nonce = nonce_from_response(&rsp);
+        let status = rsp.status();
+        match status.is_client_error() || status.is_server_error() {
+            false => Ok(rsp.text().await?),
+            true => Err(rsp.json::<Problem>().await?.into()),
+        }
+    }
+
+    pub async fn challenge(&mut self, challenge_url: &str) -> Result<Challenge, Error> {
+        self.account.get(&mut self.nonce, challenge_url).await
+    }
+
+    pub async fn state(&mut self) -> Result<OrderState, Error> {
+        self.account.get(&mut self.nonce, &self.order_url).await
+    }
+}
+
+#[derive(Clone)]
+pub struct Account {
+    inner: Arc<AccountInner>,
+}
+
+impl Account {
+    pub async fn create(account: &NewAccount<'_>, server_url: &str) -> Result<Account, Error> {
+        let client = client()?;
+        let urls = client.get(server_url).send().await?;
+        let client = Client {
+            client,
+            urls: urls.json().await?,
+        };
+
+        let key = Key::generate()?;
+        let nonce = client.nonce().await?;
+        let header = key.key_header(&nonce, &client.urls.new_account);
+        let body = key.signed_json(Some(account), header)?;
+
+        let rsp = client
+            .client
+            .post(&client.urls.new_account)
+            .header(CONTENT_TYPE, JOSE_JSON)
+            .body(body)
+            .send()
+            .await?;
+
+        let account_url = rsp
+            .headers()
+            .get(LOCATION)
+            .and_then(|hv| hv.to_str().ok())
+            .map(|s| s.to_owned());
+
+        let status = rsp.status();
+        if status.is_client_error() || status.is_server_error() {
+            return Err(rsp.json::<Problem>().await?.into());
+        }
+
+        Ok(Self {
+            inner: Arc::new(AccountInner {
+                client,
+                key,
+                id: account_url.ok_or("failed to get account URL")?,
+            }),
+        })
+    }
+
+    pub async fn new_order<'a>(
+        &'a self,
+        order: &NewOrder<'_>,
+    ) -> Result<(Order, OrderState), Error> {
+        let rsp = self
+            .inner
+            .post(Some(order), None, &self.inner.client.urls.new_order)
+            .await?;
+
+        let nonce = nonce_from_response(&rsp);
+        let order_url = rsp
+            .headers()
+            .get(LOCATION)
+            .and_then(|hv| hv.to_str().ok())
+            .map(|s| s.to_owned());
+
+        let status = Problem::check(rsp).await?;
+        Ok((
+            Order {
+                account: self.inner.clone(),
+                nonce,
+                order_url: order_url.ok_or("no order URL found")?,
+            },
+            status,
+        ))
+    }
+}
+
+impl<'de> Deserialize<'de> for Account {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let creds = AccountCredentials::deserialize(deserializer)?;
+        let pkcs8_der = base64::decode_config(&creds.key_pkcs8, URL_SAFE_NO_PAD).map_err(|_| {
+            D::Error::invalid_value(
+                Unexpected::Str(&creds.key_pkcs8),
+                &"unable to base64-decode key",
+            )
+        })?;
+
+        Ok(Self {
+            inner: Arc::new(AccountInner {
+                key: Key::from_pkcs8_der(pkcs8_der).map_err(|_| {
+                    D::Error::invalid_value(
+                        Unexpected::Str(&creds.key_pkcs8),
+                        &"unable to parse key",
+                    )
+                })?,
+                client: Client {
+                    client: client().map_err(D::Error::custom)?,
+                    urls: creds.urls.clone(),
+                },
+                id: creds.id.clone(),
+            }),
+        })
+    }
+}
+
+impl Serialize for Account {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        AccountCredentials {
+            id: self.inner.id.clone(),
+            key_pkcs8: base64::encode_config(&self.inner.key.pkcs8_der, URL_SAFE_NO_PAD),
+            urls: self.inner.client.urls.clone(),
+        }
+        .serialize(serializer)
+    }
+}
+
+struct AccountInner {
+    client: Client,
+    key: Key,
+    id: String,
+}
+
+impl AccountInner {
+    async fn get<T: DeserializeOwned>(
+        &self,
+        nonce: &mut Option<String>,
+        url: &str,
+    ) -> Result<T, Error> {
+        let rsp = self.post(None::<&Empty>, nonce.take(), url).await?;
+        *nonce = nonce_from_response(&rsp);
+        Ok(Problem::check(rsp).await?)
+    }
+
+    async fn post(
+        &self,
+        payload: Option<&impl Serialize>,
+        nonce: Option<String>,
+        url: &str,
+    ) -> Result<Response, Error> {
+        let nonce = match nonce {
+            Some(nonce) => nonce,
+            None => self.client.nonce().await?,
+        };
+
+        let header = self.key_id_header(&nonce, url);
+        let body = self.key.signed_json(payload, header)?;
+        Ok(self
+            .client
+            .client
+            .post(url)
+            .header(CONTENT_TYPE, JOSE_JSON)
+            .body(body)
+            .send()
+            .await?)
+    }
+
+    fn key_id_header<'n, 'u: 'n, 'a: 'u>(&'a self, nonce: &'n str, url: &'u str) -> Header<'n> {
+        Header {
+            alg: self.key.signing_algorithm,
+            key: KeyOrKeyId::KeyId(&self.id),
+            nonce,
+            url,
+        }
+    }
+}
+
+#[derive(Debug)]
+struct Client {
+    client: reqwest::Client,
+    urls: DirectoryUrls,
+}
+
+impl Client {
+    async fn nonce(&self) -> Result<String, Error> {
+        let future = self.client.head(&self.urls.new_nonce).send();
+        match nonce_from_response(&future.await?) {
+            Some(nonce) => Ok(nonce),
+            None => Err("no nonce found".into()),
+        }
+    }
+}
+
+struct Key {
+    rng: SystemRandom,
+    signing_algorithm: SigningAlgorithm,
+    inner: EcdsaKeyPair,
+    pkcs8_der: Vec<u8>,
+    thumb: String,
+}
+
+impl Key {
+    fn generate() -> Result<Self, Error> {
+        let rng = SystemRandom::new();
+        let pkcs8 = EcdsaKeyPair::generate_pkcs8(&ECDSA_P256_SHA256_FIXED_SIGNING, &rng)?;
+        let key = EcdsaKeyPair::from_pkcs8(&ECDSA_P256_SHA256_FIXED_SIGNING, pkcs8.as_ref())?;
+        let thumb = base64::encode_config(Jwk::thumb_sha256(&key)?, URL_SAFE_NO_PAD);
+
+        Ok(Self {
+            rng,
+            signing_algorithm: SigningAlgorithm::Es256,
+            inner: key,
+            pkcs8_der: pkcs8.as_ref().to_vec(),
+            thumb,
+        })
+    }
+
+    fn from_pkcs8_der(pkcs8_der: Vec<u8>) -> Result<Self, Error> {
+        let key = EcdsaKeyPair::from_pkcs8(&ECDSA_P256_SHA256_FIXED_SIGNING, &pkcs8_der)?;
+        let thumb = base64::encode_config(Jwk::thumb_sha256(&key)?, URL_SAFE_NO_PAD);
+
+        Ok(Self {
+            rng: SystemRandom::new(),
+            signing_algorithm: SigningAlgorithm::Es256,
+            inner: key,
+            pkcs8_der,
+            thumb,
+        })
+    }
+
+    fn signed_json(
+        &self,
+        payload: Option<&impl Serialize>,
+        protected: Header<'_>,
+    ) -> Result<Body, Error> {
+        let protected = base64(&protected)?;
+        let payload = match payload {
+            Some(data) => base64(&data)?,
+            None => String::new(),
+        };
+
+        let combined = format!("{}.{}", protected, payload);
+        let signature = self.inner.sign(&self.rng, combined.as_bytes())?;
+        Ok(Body::from(serde_json::to_vec(&JoseJson {
+            protected,
+            payload,
+            signature: base64::encode_config(signature.as_ref(), URL_SAFE_NO_PAD),
+        })?))
+    }
+
+    fn key_header<'n, 'u: 'n, 'k: 'u>(&'k self, nonce: &'n str, url: &'u str) -> Header<'n> {
+        Header {
+            alg: self.signing_algorithm,
+            key: KeyOrKeyId::from_key(&self.inner),
+            nonce,
+            url,
+        }
+    }
+}
+
+fn nonce_from_response(rsp: &Response) -> Option<String> {
+    rsp.headers()
+        .get(REPLAY_NONCE)
+        .and_then(|hv| String::from_utf8(hv.as_ref().to_vec()).ok())
+}
+
+fn base64(data: &impl Serialize) -> Result<String, serde_json::Error> {
+    Ok(base64::encode_config(
+        serde_json::to_vec(data)?,
+        URL_SAFE_NO_PAD,
+    ))
+}
+
+fn client() -> Result<reqwest::Client, reqwest::Error> {
+    reqwest::Client::builder().redirect(Policy::none()).build()
+}
+
+const JOSE_JSON: &str = "application/jose+json";
+const REPLAY_NONCE: &str = "Replay-Nonce";
diff --git a/src/types.rs b/src/types.rs
new file mode 100644
index 0000000..10ef073
--- /dev/null
+++ b/src/types.rs
@@ -0,0 +1,286 @@
+use std::fmt;
+
+use base64::URL_SAFE_NO_PAD;
+use reqwest::Response;
+use ring::digest::{digest, Digest, SHA256};
+use ring::signature::{EcdsaKeyPair, KeyPair};
+use serde::de::DeserializeOwned;
+use serde::{Deserialize, Serialize};
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum Error {
+    #[error("API error")]
+    Api(#[from] Problem),
+    #[error("base64 decoding failed")]
+    Base64(#[from] base64::DecodeError),
+    #[error("cryptographic operation failed")]
+    Crypto(#[from] ring::error::Unspecified),
+    #[error("invalid key bytes")]
+    CryptoKey(#[from] ring::error::KeyRejected),
+    #[error("HTTP request failure")]
+    Http(#[from] reqwest::Error),
+    #[error("failed to (de)serialize JSON")]
+    Json(#[from] serde_json::Error),
+    #[error("missing data: {0}")]
+    Str(&'static str),
+}
+
+impl From<&'static str> for Error {
+    fn from(s: &'static str) -> Self {
+        Error::Str(s)
+    }
+}
+
+#[derive(Deserialize, Serialize)]
+pub(crate) struct AccountCredentials {
+    pub(crate) id: String,
+    pub(crate) key_pkcs8: String,
+    pub(crate) urls: DirectoryUrls,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct Problem {
+    pub r#type: String,
+    pub detail: String,
+    pub status: u16,
+}
+
+impl Problem {
+    pub(crate) async fn check<T: DeserializeOwned>(rsp: Response) -> Result<T, Error> {
+        let status = rsp.status();
+        match status.is_client_error() || status.is_server_error() {
+            false => Ok(rsp.json().await?),
+            true => Err(rsp.json::<Self>().await?.into()),
+        }
+    }
+}
+
+impl fmt::Display for Problem {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "API error: {} ({})", self.detail, self.r#type)
+    }
+}
+
+impl std::error::Error for Problem {}
+
+pub struct KeyAuthorization(pub(crate) String);
+
+impl KeyAuthorization {
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
+
+    pub fn dns_value(&self) -> String {
+        base64::encode_config(digest(&SHA256, self.0.as_bytes()), URL_SAFE_NO_PAD)
+    }
+}
+
+impl fmt::Debug for KeyAuthorization {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("KeyAuthorization").finish()
+    }
+}
+
+#[derive(Debug, Serialize)]
+pub(crate) struct FinalizeRequest {
+    csr: String,
+}
+
+impl FinalizeRequest {
+    pub(crate) fn new(csr_der: &[u8]) -> Self {
+        Self {
+            csr: base64::encode_config(csr_der, URL_SAFE_NO_PAD),
+        }
+    }
+}
+
+#[derive(Debug, Serialize)]
+pub(crate) struct Header<'a> {
+    pub(crate) alg: SigningAlgorithm,
+    #[serde(flatten)]
+    pub(crate) key: KeyOrKeyId<'a>,
+    pub(crate) nonce: &'a str,
+    pub(crate) url: &'a str,
+}
+
+#[derive(Debug, Serialize)]
+pub(crate) enum KeyOrKeyId<'a> {
+    #[serde(rename = "jwk")]
+    Key(Jwk),
+    #[serde(rename = "kid")]
+    KeyId(&'a str),
+}
+
+impl<'a> KeyOrKeyId<'a> {
+    pub(crate) fn from_key(key: &EcdsaKeyPair) -> KeyOrKeyId<'static> {
+        KeyOrKeyId::Key(Jwk::new(key))
+    }
+}
+
+#[derive(Debug, Serialize)]
+pub(crate) struct Jwk {
+    alg: SigningAlgorithm,
+    crv: &'static str,
+    kty: &'static str,
+    r#use: &'static str,
+    x: String,
+    y: String,
+}
+
+impl Jwk {
+    pub(crate) fn new(key: &EcdsaKeyPair) -> Self {
+        let (x, y) = key.public_key().as_ref()[1..].split_at(32);
+        Self {
+            alg: SigningAlgorithm::Es256,
+            crv: "P-256",
+            kty: "EC",
+            r#use: "sig",
+            x: base64::encode_config(x, URL_SAFE_NO_PAD),
+            y: base64::encode_config(y, URL_SAFE_NO_PAD),
+        }
+    }
+
+    pub(crate) fn thumb_sha256(key: &EcdsaKeyPair) -> Result<Digest, serde_json::Error> {
+        let jwk = Self::new(key);
+        Ok(digest(
+            &SHA256,
+            &serde_json::to_vec(&JwkThumb {
+                crv: jwk.crv,
+                kty: jwk.kty,
+                x: &jwk.x,
+                y: &jwk.y,
+            })?,
+        ))
+    }
+}
+
+#[derive(Debug, Serialize)]
+struct JwkThumb<'a> {
+    crv: &'a str,
+    kty: &'a str,
+    x: &'a str,
+    y: &'a str,
+}
+
+#[derive(Debug, Deserialize)]
+pub struct Challenge {
+    pub r#type: ChallengeType,
+    pub url: String,
+    pub token: String,
+    pub status: ChallengeStatus,
+    pub error: Option<Problem>,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct OrderState {
+    pub status: OrderStatus,
+    pub authorizations: Vec<String>,
+    pub error: Option<Problem>,
+    pub finalize: String,
+    pub certificate: Option<String>,
+}
+
+#[derive(Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct NewOrder<'a> {
+    pub identifiers: &'a [Identifier],
+}
+
+#[derive(Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct NewAccount<'a> {
+    pub contact: &'a [&'a str],
+    pub terms_of_service_agreed: bool,
+    pub only_return_existing: bool,
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub(crate) struct DirectoryUrls {
+    pub(crate) new_nonce: String,
+    pub(crate) new_account: String,
+    pub(crate) new_order: String,
+}
+
+#[derive(Serialize)]
+pub(crate) struct JoseJson {
+    pub(crate) protected: String,
+    pub(crate) payload: String,
+    pub(crate) signature: String,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(tag = "status", rename_all = "camelCase")]
+pub enum Authorization {
+    Pending {
+        identifier: Identifier,
+        challenges: Vec<Challenge>,
+    },
+    Valid,
+    Invalid,
+    Revoked,
+    Expired,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+#[serde(tag = "type", content = "value", rename_all = "camelCase")]
+pub enum Identifier {
+    Dns(String),
+}
+
+#[derive(Clone, Copy, Debug, Deserialize, Eq, PartialEq)]
+pub enum ChallengeType {
+    #[serde(rename = "http-01")]
+    Http01,
+    #[serde(rename = "dns-01")]
+    Dns01,
+    #[serde(rename = "tls-alpn-01")]
+    TlsAlpn01,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub enum ChallengeStatus {
+    Pending,
+    Processing,
+    Valid,
+    Invalid,
+}
+
+#[derive(Debug, Deserialize, PartialEq)]
+#[serde(rename_all = "camelCase")]
+pub enum OrderStatus {
+    Pending,
+    Ready,
+    Processing,
+    Valid,
+    Invalid,
+}
+
+#[derive(Clone, Copy, Debug)]
+pub enum LetsEncrypt {
+    Production,
+    Staging,
+}
+
+impl LetsEncrypt {
+    pub fn url(&self) -> &'static str {
+        match self {
+            LetsEncrypt::Production => "https://acme-v02.api.letsencrypt.org/directory",
+            LetsEncrypt::Staging => "https://acme-staging-v02.api.letsencrypt.org/directory",
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, Serialize)]
+#[serde(rename_all = "UPPERCASE")]
+pub(crate) enum SigningAlgorithm {
+    /// ECDSA using P-256 and SHA-256
+    Es256,
+}
+
+#[derive(Debug, Serialize)]
+pub(crate) struct Empty {}