grpc-plugin: Generate mTLS certificates and use them in grpc

plugins/grpc-plugin/src/main.rs

@@ -5,10 +5,14 @@ use log::{debug, warn};
 use std::net::SocketAddr;
 use std::path::{Path, PathBuf};
 
+mod tls;
+
 #[derive(Clone, Debug)]
 struct PluginState {
     rpc_path: PathBuf,
     bind_address: SocketAddr,
+    identity: tls::Identity,
+    ca_cert: Vec<u8>,
 }
 
 #[tokio::main]
@@ -17,9 +21,14 @@ async fn main() -> Result<()> {
     let path = Path::new("lightning-rpc");
     let addr: SocketAddr = "0.0.0.0:50051".parse().unwrap();
 
+    let directory = std::env::current_dir()?;
+    let (identity, ca_cert) = tls::init(&directory)?;
+
     let state = PluginState {
         rpc_path: path.into(),
         bind_address: addr,
+        identity,
+        ca_cert,
     };
 
     let (plugin, i) = Builder::new(state.clone(), tokio::io::stdin(), tokio::io::stdout()).build();
@@ -38,7 +47,17 @@ async fn run_interface(state: PluginState) -> Result<()> {
         "Connecting to {:?} and serving grpc on {:?}",
         &state.rpc_path, &state.bind_address
     );
+
+    let identity = state.identity.to_tonic_identity();
+    let ca_cert = tonic::transport::Certificate::from_pem(state.ca_cert);
+
+    let tls = tonic::transport::ServerTlsConfig::new()
+        .identity(identity)
+        .client_ca_root(ca_cert);
+
     tonic::transport::Server::builder()
+        .tls_config(tls)
+        .context("configuring tls")?
         .add_service(NodeServer::new(
             cln_grpc::Server::new(&state.rpc_path)
                 .await

plugins/grpc-plugin/src/tls.rs

@@ -0,0 +1,107 @@
+//! Utilities to manage TLS certificates.
+use anyhow::{Context, Result};
+use log::debug;
+use rcgen::{Certificate, KeyPair};
+use std::path::Path;
+
+/// Just a wrapper around a certificate and an associated keypair.
+#[derive(Clone, Debug)]
+pub(crate) struct Identity {
+    key: Vec<u8>,
+    certificate: Vec<u8>,
+}
+
+impl Identity {
+    fn to_certificate(&self) -> Result<Certificate> {
+        let keystr = String::from_utf8_lossy(&self.key);
+        let key = KeyPair::from_pem(&keystr)?;
+        let certstr = String::from_utf8_lossy(&self.certificate);
+        let params = rcgen::CertificateParams::from_ca_cert_pem(&certstr, key)?;
+        let cert = Certificate::from_params(params)?;
+        Ok(cert)
+    }
+
+    pub fn to_tonic_identity(&self) -> tonic::transport::Identity {
+        tonic::transport::Identity::from_pem(&self.certificate, &self.key)
+    }
+}
+
+/// Ensure that we have a certificate authority, and child keypairs
+/// and certificates for the server and the client. It'll generate
+/// them in the provided `directory`. The following files are
+/// included:
+///
+/// - `ca.pem`: The self-signed certificate of the CA
+/// - `ca-key.pem`: The key used by the CA to sign certificates
+/// - `server.pem`: The server certificate, signed by the CA
+/// - `server-key.pem`: The server private key
+/// - `client.pem`: The client certificate, signed by the CA
+/// - `client-key.pem`: The client private key
+///
+/// The `grpc-plugin` will use the `server.pem` certificate, while a
+/// client is supposed to use the `client.pem` and associated
+/// keys. Notice that this isn't strictly necessary since the server
+/// will accept any client that is signed by the CA. In future we
+/// might add runes, making the distinction more important.
+///
+/// Returns the server identity and the root CA certificate.
+pub(crate) fn init(directory: &Path) -> Result<(Identity, Vec<u8>)> {
+    let ca = generate_or_load_identity("cln Root CA", directory, "ca", None)?;
+    let server = generate_or_load_identity("cln grpc Server", directory, "server", Some(&ca))?;
+    let _client = generate_or_load_identity("cln grpc Client", directory, "client", Some(&ca))?;
+    Ok((server, ca.certificate))
+}
+
+/// Generate a given identity
+fn generate_or_load_identity(
+    name: &str,
+    directory: &Path,
+    filename: &str,
+    parent: Option<&Identity>,
+) -> Result<Identity> {
+    // Just our naming convention here.
+    let cert_path = directory.join(format!("{}.pem", filename));
+    let key_path = directory.join(format!("{}-key.pem", filename));
+    // Did we have to generate a new key? In that case we also need to
+    // regenerate the certificate
+    if !key_path.exists() || !cert_path.exists() {
+        debug!(
+            "Generating a new keypair in {:?}, it didn't exist",
+            &key_path
+        );
+        let keypair = KeyPair::generate(&rcgen::PKCS_ECDSA_P256_SHA256)?;
+        std::fs::write(&key_path, keypair.serialize_pem())?;
+        debug!(
+            "Generating a new certificate for key {:?} at {:?}",
+            &key_path, &cert_path
+        );
+
+        // Configure the certificate we want.
+        let subject_alt_names = vec!["cln".to_string(), "localhost".to_string()];
+        let mut params = rcgen::CertificateParams::new(subject_alt_names);
+        params.key_pair = Some(keypair);
+        params.alg = &rcgen::PKCS_ECDSA_P256_SHA256;
+        if parent.is_none() {
+            params.is_ca = rcgen::IsCa::Ca(rcgen::BasicConstraints::Unconstrained);
+        } else {
+            params.is_ca = rcgen::IsCa::SelfSignedOnly;
+        }
+        params
+            .distinguished_name
+            .push(rcgen::DnType::CommonName, name);
+
+        let cert = Certificate::from_params(params)?;
+        std::fs::write(
+            &cert_path,
+            match parent {
+                None => cert.serialize_pem()?,
+                Some(ca) => cert.serialize_pem_with_signer(&ca.to_certificate()?)?,
+            },
+        )
+        .context("writing certificate to file")?;
+    }
+
+    let key = std::fs::read(&key_path)?;
+    let certificate = std::fs::read(cert_path)?;
+    Ok(Identity { certificate, key })
+}