add external account binding

Functionality was added as a additional setter function, which hopefully
prevents any breakages. Since a placeholder Option an the AccountData
was already present, but has never been used, replacing the field with
an Option of a fully defined type should also be minimally intrusive.

Signed-off-by: Folke Gleumes <f.gleumes@proxmox.com>

src/account.rs

@@ -11,8 +11,9 @@ use serde_json::Value;
 use crate::authorization::{Authorization, GetAuthorization};
 use crate::b64u;
 use crate::directory::Directory;
+use crate::eab::ExternalAccountBinding;
 use crate::jws::Jws;
-use crate::key::PublicKey;
+use crate::key::{Jwk, PublicKey};
 use crate::order::{NewOrder, Order, OrderData};
 use crate::request::Request;
 use crate::Error;
@@ -336,10 +337,9 @@ pub struct AccountData {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub terms_of_service_agreed: Option<bool>,
 
-    /// External account information. This is currently not directly supported in any way and only
-    /// stored to completeness.
+    /// External account information.
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub external_account_binding: Option<Value>,
+    pub external_account_binding: Option<ExternalAccountBinding>,
 
     /// This is only used by the client when querying an account.
     #[serde(default = "default_true", skip_serializing_if = "is_false")]
@@ -375,6 +375,7 @@ pub struct AccountCreator {
     contact: Vec<String>,
     terms_of_service_agreed: bool,
     key: Option<PKey<Private>>,
+    eab_credentials: Option<(String, PKey<Private>)>,
 }
 
 impl AccountCreator {
@@ -402,6 +403,13 @@ impl AccountCreator {
         self
     }
 
+    /// Set the EAB credentials for the account registration
+    pub fn set_eab_credentials(mut self, kid: String, hmac_key: String) -> Result<Self, Error> {
+        let hmac_key = PKey::hmac(&base64::decode(hmac_key)?)?;
+        self.eab_credentials = Some((kid, hmac_key));
+        Ok(self)
+    }
+
     /// Generate a new RSA key of the specified key size.
     pub fn generate_rsa_key(self, bits: u32) -> Result<Self, Error> {
         let key = openssl::rsa::Rsa::generate(bits)?;
@@ -431,6 +439,15 @@ impl AccountCreator {
     /// [`response`](AccountCreator::response()) will render the account unusable!
     pub fn request(&self, directory: &Directory, nonce: &str) -> Result<Request, Error> {
         let key = self.key.as_deref().ok_or(Error::MissingKey)?;
+        let url = directory.new_account_url();
+
+        let external_account_binding = self
+            .eab_credentials
+            .as_ref()
+            .map(|cred| {
+                ExternalAccountBinding::new(&cred.0, &cred.1, Jwk::try_from(key)?, url.to_string())
+            })
+            .transpose()?;
 
         let data = AccountData {
             orders: None,
@@ -441,12 +458,11 @@ impl AccountCreator {
             } else {
                 None
             },
-            external_account_binding: None,
+            external_account_binding,
             only_return_existing: false,
             extra: HashMap::new(),
         };
 
-        let url = directory.new_account_url();
         let body = serde_json::to_string(&Jws::new(
             key,
             None,

src/eab.rs

@@ -0,0 +1,66 @@
+use openssl::hash::MessageDigest;
+use openssl::pkey::{HasPrivate, PKeyRef};
+use openssl::sign::Signer;
+use serde::{Deserialize, Serialize};
+
+use crate::key::Jwk;
+use crate::{b64u, Error};
+
+#[derive(Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+struct Protected {
+    alg: &'static str,
+    url: String,
+    kid: String,
+}
+
+#[derive(Debug, Serialize, Deserialize, Clone)]
+#[serde(rename_all = "camelCase")]
+pub struct ExternalAccountBinding {
+    protected: String,
+    payload: String,
+    signature: String,
+}
+
+impl ExternalAccountBinding {
+    pub fn new<P>(
+        eab_kid: &str,
+        eab_hmac_key: &PKeyRef<P>,
+        jwk: Jwk,
+        url: String,
+    ) -> Result<Self, Error>
+    where
+        P: HasPrivate,
+    {
+        let protected = Protected {
+            alg: "HS256",
+            kid: eab_kid.to_string(),
+            url,
+        };
+        let payload = b64u::encode(serde_json::to_string(&jwk)?.as_bytes());
+        let protected_data = b64u::encode(serde_json::to_string(&protected)?.as_bytes());
+        let signature = {
+            let protected = protected_data.as_bytes();
+            let payload = payload.as_bytes();
+            Self::sign_hmac(eab_hmac_key, protected, payload)?
+        };
+
+        let signature = b64u::encode(&signature);
+        Ok(ExternalAccountBinding {
+            protected: protected_data,
+            payload,
+            signature,
+        })
+    }
+
+    fn sign_hmac<P>(key: &PKeyRef<P>, protected: &[u8], payload: &[u8]) -> Result<Vec<u8>, Error>
+    where
+        P: HasPrivate,
+    {
+        let mut signer = Signer::new(MessageDigest::sha256(), key)?;
+        signer.update(protected)?;
+        signer.update(b".")?;
+        signer.update(payload)?;
+        Ok(signer.sign_to_vec()?)
+    }
+}

src/error.rs

@@ -59,6 +59,9 @@ pub enum Error {
     /// An otherwise uncaught serde error happened.
     Json(serde_json::Error),
 
+    /// Failed to parse
+    BadBase64(base64::DecodeError),
+
     /// Can be used by the user for textual error messages without having to downcast to regular
     /// acme errors.
     Custom(String),
@@ -121,6 +124,7 @@ impl fmt::Display for Error {
             Error::HttpClient(err) => fmt::Display::fmt(err, f),
             Error::Client(err) => fmt::Display::fmt(err, f),
             Error::Csr(err) => fmt::Display::fmt(err, f),
+            Error::BadBase64(err) => fmt::Display::fmt(err, f),
         }
     }
 }
@@ -142,3 +146,9 @@ impl From<crate::request::ErrorResponse> for Error {
         Error::Api(e)
     }
 }
+
+impl From<base64::DecodeError> for Error {
+    fn from(e: base64::DecodeError) -> Self {
+        Error::BadBase64(e)
+    }
+}

src/lib.rs

@@ -14,6 +14,7 @@
 #![deny(missing_docs)]
 
 mod b64u;
+mod eab;
 mod json;
 mod jws;
 mod key;