Initial commit

server/.editorconfig

@@ -0,0 +1,10 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[**.rs]
+max_line_length = 79

server/.gitattributes

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+Cargo.lock -diff

server/.gitignore

@@ -0,0 +1,4 @@
+/target
+/config.toml
+/machine_ids.json
+/host_ca_key*

server/Cargo.toml

@@ -0,0 +1,33 @@
+[package]
+name = "sshca"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+argh = "0.1.12"
+argon2 = { version = "0.5.2", default-features = false, features = ["alloc"] }
+axum = { version = "0.6.20", features = ["multipart", "headers", "json"] }
+dirs = "5.0.1"
+jsonwebtoken = { version = "8.3.0", default-features = false }
+rand_core = { version = "0.6.4", features = ["getrandom"] }
+serde = { version = "1.0.190", features = ["derive"] }
+serde_json = "1.0.108"
+ssh-key = { version = "0.6.2", features = ["serde", "ed25519", "getrandom"] }
+tokio = { version = "1.33.0", features = ["rt", "macros", "net", "signal", "fs", "io-util"] }
+toml = "0.8.6"
+tracing = { version = "0.1.40", features = ["log"] }
+tracing-subscriber = { version = "0.3.17", features = ["env-filter"] }
+uuid = "1.5.0"
+virt = { version = "0.3.1", optional = true }
+
+[features]
+default = ["libvirt"]
+libvirt = ["dep:virt"]
+
+[dev-dependencies]
+form-data-builder = "1.0.1"
+hyper = "0.14.27"
+serial_test = "2.0.0"
+tempfile = "3.8.1"
+tower = { version = "0.4.13", features = ["util"] }
+

server/rustfmt.toml

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+max_width  = 79

server/src/auth.rs

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+//! Authentication
+//!
+//! SSHCA authentication is handled using JWTs.  Each request must include a
+//! proper token, with the target system's hostname as the subject and issuer,
+//! signed by that system's machine ID.
+//!
+//! To identify identify the subject of a token, use [`get_token_subject`].
+//! This function will return the hostname specified in the token; use this
+//! to look up the machine ID of the system.  Then, use [`validate_token`] to
+//! validate the token.
+
+use argon2::Argon2;
+use jsonwebtoken::errors::Result;
+use jsonwebtoken::{decode, Algorithm, DecodingKey, TokenData, Validation};
+use rand_core::{OsRng, RngCore};
+use serde::Deserialize;
+use tracing::error;
+use uuid::Uuid;
+
+/// JWT Token Claims
+#[derive(Debug, Deserialize)]
+pub struct Claims {
+    /// Token subject (machine hostname)
+    pub sub: String,
+}
+
+/// Extract the subject from the token
+///
+/// This function takes a JWT  string and returns the value of the `sub` claim.
+/// The signature of the token is not validated, but if the token has expired,
+/// an error is returned.
+pub fn get_token_subject(token: &str) -> Result<String> {
+    let mut v = Validation::new(Algorithm::HS256);
+    v.insecure_disable_signature_validation();
+    v.set_required_spec_claims(&["sub"]);
+    let k = DecodingKey::from_secret(b"");
+    let data: TokenData<Claims> = decode(token, &k, &v)?;
+    Ok(data.claims.sub)
+}
+
+/// Validate a token
+///
+/// This function validates a JWT for the specified hostname and its
+/// corresponding machine ID.  The token is valid if it is issued for the
+/// specified hostname by the same, has an audience matching the value of the
+/// `service` argument, and is within its validity period (not before/expires).
+/// The token must be signed with HMAC-SHA256 using the host's machine ID as
+/// the secret key.
+pub fn validate_token(
+    token: &str,
+    hostname: &str,
+    machine_id: &Uuid,
+    service: &str,
+) -> Result<Claims> {
+    let mut v = Validation::new(Algorithm::HS256);
+    v.validate_nbf = true;
+    v.set_issuer(&[hostname]);
+    v.set_audience(&[service]);
+    let mut secret = [0u8; 32];
+    if let Err(e) = Argon2::default().hash_password_into(
+        machine_id.as_bytes(),
+        hostname.as_bytes(),
+        &mut secret,
+    ) {
+        error!("Could not derive token secret: {}", e);
+        OsRng.fill_bytes(&mut secret);
+    }
+    let k = DecodingKey::from_secret(&secret);
+    let data: TokenData<Claims> = decode(token, &k, &v)?;
+    Ok(data.claims)
+}
+
+#[cfg(test)]
+pub(crate) mod test {
+    use std::time;
+
+    use jsonwebtoken::{encode, EncodingKey};
+    use serde::Serialize;
+    use uuid::uuid;
+
+    use super::*;
+
+    #[derive(Debug, Serialize)]
+    struct TestClaims {
+        sub: String,
+        iss: String,
+        aud: String,
+        iat: u64,
+        nbf: u64,
+        exp: u64,
+    }
+
+    pub(crate) fn make_token(hostname: &str, machine_id: Uuid) -> String {
+        let now = time::SystemTime::now()
+            .duration_since(time::UNIX_EPOCH)
+            .unwrap()
+            .as_secs();
+        let claims = TestClaims {
+            sub: hostname.into(),
+            iss: hostname.into(),
+            aud: "sshca.example.org".into(),
+            nbf: now - 60,
+            iat: now,
+            exp: now + 60,
+        };
+        let mut secret = [0u8; 32];
+        Argon2::default()
+            .hash_password_into(
+                machine_id.as_bytes(),
+                hostname.as_bytes(),
+                &mut secret,
+            )
+            .unwrap();
+        let key = EncodingKey::from_secret(&secret);
+        encode(&Default::default(), &claims, &key).unwrap()
+    }
+
+    #[test]
+    fn test_get_token_subject() {
+        let hostname = "web0.example.org";
+        let machine_id = uuid!("890ec6fe-e6c2-4524-bec0-d474af8aa506");
+        let token = make_token(hostname, machine_id);
+        let sub = get_token_subject(&token).unwrap();
+        assert_eq!(sub, hostname);
+    }
+
+    #[test]
+    fn test_validate_token() {
+        let hostname = "file0.example.org";
+
+        let machine_id = uuid!("9afd42e5-4ac3-4530-90c4-191869063ef9");
+        let token = make_token(hostname, machine_id);
+        validate_token(&token, hostname, &machine_id, "sshca.example.org")
+            .unwrap();
+    }
+}

server/src/ca.rs

@@ -0,0 +1,171 @@
+//! SSH certificate authority
+use std::path::Path;
+use std::time::{Duration, SystemTime, UNIX_EPOCH};
+
+use ssh_key::certificate::{Builder, CertType};
+use ssh_key::rand_core::OsRng;
+use ssh_key::{Certificate, PrivateKey, PublicKey};
+use tokio::fs::File;
+use tokio::io::AsyncReadExt;
+use tracing::debug;
+
+#[derive(Debug)]
+pub enum CertError {
+    SystemTime(std::time::SystemTimeError),
+    SshKey(ssh_key::Error),
+}
+
+impl From<std::time::SystemTimeError> for CertError {
+    fn from(e: std::time::SystemTimeError) -> Self {
+        Self::SystemTime(e)
+    }
+}
+
+impl From<ssh_key::Error> for CertError {
+    fn from(e: ssh_key::Error) -> Self {
+        Self::SshKey(e)
+    }
+}
+
+impl std::fmt::Display for CertError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            Self::SystemTime(e) => write!(f, "Invalid time: {}", e),
+            Self::SshKey(e) => write!(f, "SSH key error: {}", e),
+        }
+    }
+}
+
+impl std::error::Error for CertError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::SystemTime(e) => Some(e),
+            Self::SshKey(e) => Some(e),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum LoadKeyError {
+    Utf8(std::str::Utf8Error),
+    Io(std::io::Error),
+    SshKey(ssh_key::Error),
+}
+
+impl From<std::str::Utf8Error> for LoadKeyError {
+    fn from(e: std::str::Utf8Error) -> Self {
+        Self::Utf8(e)
+    }
+}
+
+impl From<std::io::Error> for LoadKeyError {
+    fn from(e: std::io::Error) -> Self {
+        Self::Io(e)
+    }
+}
+
+impl From<ssh_key::Error> for LoadKeyError {
+    fn from(e: ssh_key::Error) -> Self {
+        Self::SshKey(e)
+    }
+}
+
+impl std::fmt::Display for LoadKeyError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            Self::Utf8(e) => write!(f, "Invalid key: {}", e),
+            Self::Io(e) => write!(f, "Could not read key file: {}", e),
+            Self::SshKey(e) => write!(f, "Could not parse SSH key: {}", e),
+        }
+    }
+}
+
+impl std::error::Error for LoadKeyError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::Utf8(e) => Some(e),
+            Self::Io(e) => Some(e),
+            Self::SshKey(e) => Some(e),
+        }
+    }
+}
+
+/// Load an SSH private key from a file
+pub async fn load_private_key<P>(path: P) -> Result<PrivateKey, LoadKeyError>
+where
+    P: AsRef<Path>,
+{
+    let mut data = Vec::new();
+    debug!("Loading private key from {}", path.as_ref().display());
+    let mut f = File::open(path).await?;
+    f.read_to_end(&mut data).await?;
+    parse_private_key(&data)
+}
+
+/// Parse an SSH private key from a slice of bytes
+pub fn parse_private_key(data: &[u8]) -> Result<PrivateKey, LoadKeyError> {
+    Ok(PrivateKey::from_openssh(std::str::from_utf8(data)?)?)
+}
+
+/// Parse an SSH public key from a slice of bytes
+pub fn parse_public_key(data: &[u8]) -> Result<PublicKey, LoadKeyError> {
+    Ok(PublicKey::from_openssh(std::str::from_utf8(data)?)?)
+}
+
+/// Create a signed SSH certificate for a host public key
+///
+/// This function creates a signed certificate for an SSH host public
+/// key.  The certificate will be valid for the specified hostname and
+/// any alias names provided.
+pub fn sign_cert(
+    hostname: &str,
+    pubkey: &PublicKey,
+    duration: Duration,
+    privkey: &PrivateKey,
+    alias: &[&str],
+) -> Result<Certificate, CertError> {
+    let now = SystemTime::now();
+    let not_before = now.duration_since(UNIX_EPOCH)?.as_secs();
+    let not_after = not_before + duration.as_secs();
+
+    let mut builder = Builder::new_with_random_nonce(
+        &mut OsRng, pubkey, not_before, not_after,
+    )?;
+    builder.cert_type(CertType::Host)?;
+    builder.valid_principal(hostname)?;
+    for a in alias {
+        builder.valid_principal(*a)?;
+    }
+
+    Ok(builder.sign(privkey)?)
+}
+
+#[cfg(test)]
+mod test {
+    use ssh_key::Algorithm;
+
+    use super::*;
+
+    #[test]
+    fn test_sign_cert() {
+        let ca_key =
+            PrivateKey::random(&mut OsRng, Algorithm::Ed25519).unwrap();
+        let host_key =
+            PrivateKey::random(&mut OsRng, Algorithm::Ed25519).unwrap();
+        let host_pub_key = host_key.public_key();
+        let duration = Duration::from_secs(86400 * 30);
+        let hostname = "cloud0.example.org";
+        let cert = sign_cert(
+            hostname,
+            &host_pub_key,
+            duration,
+            &ca_key,
+            &["nextcloud.example.org"],
+        )
+        .unwrap();
+
+        let valid_principals = cert.valid_principals();
+        assert_eq!(valid_principals[0], "cloud0.example.org");
+        assert_eq!(valid_principals[1], "nextcloud.example.org");
+    }
+}

server/src/config.rs

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+//! Application configuration
+use std::io::ErrorKind;
+use std::path::{Path, PathBuf};
+
+use serde::Deserialize;
+use tracing::debug;
+
+/// Error returned by [`load_config`]
+#[derive(Debug)]
+pub enum ConfigError {
+    Io(std::io::Error),
+    Toml(toml::de::Error),
+}
+
+impl From<std::io::Error> for ConfigError {
+    fn from(e: std::io::Error) -> Self {
+        Self::Io(e)
+    }
+}
+
+impl From<toml::de::Error> for ConfigError {
+    fn from(e: toml::de::Error) -> Self {
+        Self::Toml(e)
+    }
+}
+
+impl std::fmt::Display for ConfigError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            Self::Io(e) => write!(f, "Could not read config file: {}", e),
+            Self::Toml(e) => write!(f, "Could not parse config: {}", e),
+        }
+    }
+}
+
+impl std::error::Error for ConfigError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::Io(e) => Some(e),
+            Self::Toml(e) => Some(e),
+        }
+    }
+}
+
+/// Host CA Configuration
+#[derive(Debug, Deserialize)]
+pub struct HostCaConfig {
+    /// Path to the Host CA private key file
+    #[serde(default = "default_host_ca_key")]
+    pub private_key_file: PathBuf,
+
+    /// Duration of issued host certificates
+    #[serde(default = "default_host_cert_duration")]
+    pub cert_duration: u64,
+}
+
+impl Default for HostCaConfig {
+    fn default() -> Self {
+        Self {
+            private_key_file: default_host_ca_key(),
+            cert_duration: default_host_cert_duration(),
+        }
+    }
+}
+
+/// CA configuration
+#[derive(Debug, Default, Deserialize)]
+pub struct CaConfig {
+    /// Host CA configuration
+    pub host: HostCaConfig,
+}
+
+/// Defines a connection to a libvirt VM host
+#[derive(Debug, Deserialize)]
+pub struct LibvirtConfig {
+    /// libvirt Connection URI
+    pub uri: String,
+}
+
+/// Top-level configuration structure
+#[derive(Debug, Deserialize)]
+pub struct Configuration {
+    /// List of libvirt connection options
+    #[serde(default)]
+    pub libvirt: Vec<LibvirtConfig>,
+    /// Path to the machine ID map JSON file
+    #[serde(default = "default_machine_ids")]
+    pub machine_ids: PathBuf,
+    /// CA configuration
+    #[serde(default)]
+    pub ca: CaConfig,
+}
+
+impl Default for Configuration {
+    fn default() -> Self {
+        Self {
+            libvirt: vec![],
+            machine_ids: default_machine_ids(),
+            ca: Default::default(),
+        }
+    }
+}
+
+fn default_config_path(basename: &str) -> PathBuf {
+    dirs::config_dir().map_or(PathBuf::from(basename), |mut p| {
+        p.push(env!("CARGO_PKG_NAME"));
+        p.push(basename);
+        p
+    })
+}
+
+fn default_machine_ids() -> PathBuf {
+    default_config_path("machine_ids.json")
+}
+
+fn default_host_ca_key() -> PathBuf {
+    default_config_path("host-ca.key")
+}
+
+fn default_host_cert_duration() -> u64 {
+    86400 * 30
+}
+
+/// Load configuration from a TOML file
+///
+/// If `path` is provided, the configuration will be loaded from the
+/// TOML file at that location.  If `path` is `None`, the path will be
+/// inferred from the XDG Configuration directory (i.e.
+/// `${XDG_CONFIG_HOME}/sshca/config.toml`).
+///
+/// If the configuration file does not exist, the default values will be
+/// used.  If any error is encountered while reading or parsing the
+/// file, a [`ConfigError`] will be returned.
+pub fn load_config<P>(path: Option<P>) -> Result<Configuration, ConfigError>
+where
+    P: AsRef<Path>,
+{
+    let path = match path {
+        Some(p) => PathBuf::from(p.as_ref()),
+        None => default_config_path("config.toml"),
+    };
+    debug!("Loading configuration from {}", path.display());
+    match std::fs::read_to_string(path) {
+        Ok(s) => Ok(toml::from_str(&s)?),
+        Err(ref e) if e.kind() == ErrorKind::NotFound => {
+            Ok(Default::default())
+        }
+        Err(e) => Err(e.into()),
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use serial_test::serial;
+
+    use super::*;
+
+    #[test]
+    #[serial]
+    fn test_default_config() {
+        std::env::remove_var("XDG_CONFIG_HOME");
+        std::env::set_var("HOME", "/home/user");
+        let config = Configuration::default();
+        assert_eq!(
+            config.machine_ids,
+            PathBuf::from("/home/user/.config/sshca/machine_ids.json"),
+        );
+        assert_eq!(config.libvirt.len(), 0);
+    }
+
+    #[test]
+    #[serial]
+    fn test_default_config_path() {
+        std::env::remove_var("XDG_CONFIG_HOME");
+        std::env::set_var("HOME", "/home/user");
+        let path = default_config_path("config.toml");
+        assert_eq!(
+            path,
+            PathBuf::from("/home/user/.config/sshca/config.toml"),
+        );
+    }
+
+    #[test]
+    #[serial]
+    fn test_default_config_path_env() {
+        std::env::set_var("XDG_CONFIG_HOME", "/etc");
+        let path = default_config_path("config.toml");
+        assert_eq!(path, PathBuf::from("/etc/sshca/config.toml"));
+    }
+
+    #[test]
+    fn test_config_toml() {
+        let config_toml = r#"
+[[libvirt]]
+uri = "qemu+ssh://vmhost0.example.org/system"
+
+[[libvirt]]
+uri = "qemu+ssh://vmhost1.example.org/system"
+"#;
+        let config: Configuration = toml::from_str(config_toml).unwrap();
+        assert_eq!(config.libvirt.len(), 2);
+        assert_eq!(
+            config.libvirt[0].uri,
+            "qemu+ssh://vmhost0.example.org/system"
+        );
+        assert_eq!(
+            config.libvirt[1].uri,
+            "qemu+ssh://vmhost1.example.org/system"
+        );
+    }
+}

server/src/lib.rs

@@ -0,0 +1,7 @@
+mod auth;
+mod ca;
+pub mod config;
+#[cfg(feature = "libvirt")]
+mod libvirt;
+mod machine_id;
+pub mod server;

server/src/libvirt.rs

@@ -0,0 +1,53 @@
+//! libvirt VM info
+use tracing::error;
+use virt::connect::Connect;
+use virt::domain::Domain;
+
+use crate::config::LibvirtConfig;
+
+/// libvirt connection wrapper with auto-disconnect
+///
+/// This structure wraps a virConnect object and automatically calls
+/// virConnectClose when it is dropped.
+struct Connection {
+    conn: Connect,
+}
+
+impl Drop for Connection {
+    fn drop(&mut self) {
+        if let Err(e) = self.conn.close() {
+            error!("Failed to close libvirt connection: {}", e);
+        }
+    }
+}
+
+/// Get the UUID of a libvirt VM
+///
+/// This function connects to the libvirt daemon specified in the provided
+/// [`LibvirtConfig`] structure and attempts to get the UUID of the virtual
+/// machine with the given name.  If the connection cannot be established, or
+/// no machine is found with that name, an error is returned.
+pub fn get_machine_id(
+    name: &str,
+    config: &LibvirtConfig,
+) -> Result<String, virt::error::Error> {
+    let conn = Connection {
+        conn: Connect::open_read_only(&config.uri)?,
+    };
+    let dom = Domain::lookup_by_name(&conn.conn, name)?;
+    dom.get_uuid_string()
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_get_machine_id() {
+        let config = LibvirtConfig {
+            uri: "test:///default".into(),
+        };
+        let machine_id = get_machine_id("test", &config).unwrap();
+        assert_eq!(&machine_id, "6695eb01-f6a4-8304-79aa-97f2502e193f");
+    }
+}

server/src/machine_id.rs

@@ -0,0 +1,108 @@
+//! Look up a known machine ID
+use std::sync::Arc;
+
+use serde_json::Value;
+use tokio::task;
+use tracing::{debug, error};
+use uuid::Uuid;
+
+use crate::config::Configuration;
+use crate::libvirt;
+
+/// Look up the machine ID for a host
+///
+/// This function will return the machine ID for a known host, either from the
+/// static map stored in a JSON file or from a libvirt VM host.  If no location
+/// has a record for the machine, `None` is returned.
+pub async fn get_machine_id(
+    hostname: &str,
+    config: Arc<Configuration>,
+) -> Option<Uuid> {
+    if let Some(v) = from_map(hostname, config.clone()).await {
+        return parse_uuid(&v);
+    }
+    #[cfg(feature = "libvirt")]
+    if let Some(v) = from_libvirt(hostname, config.clone()).await {
+        return parse_uuid(&v);
+    }
+    None
+}
+
+/// Look up a machine ID in the JSON map file
+///
+/// This function reads the machine ID map stored in the JSON file.  If the
+/// file could not be opened, is not a valid JSON object, or does not contain
+/// an entry for the specified hostname, `None` is returned.
+async fn from_map(
+    hostname: &str,
+    config: Arc<Configuration>,
+) -> Option<String> {
+    let data = match tokio::fs::read_to_string(&config.machine_ids).await {
+        Ok(d) => d,
+        Err(e) => {
+            error!("Failed to read machine ID map file: {}", e);
+            return None;
+        }
+    };
+    let res =
+        task::spawn_blocking(move || serde_json::from_str::<Value>(&data))
+            .await;
+    let map = match res {
+        Ok(Ok(r)) => r,
+        Ok(Err(e)) => {
+            error!("Error parsing machine ID map: {}", e);
+            return None;
+        }
+        Err(e) => {
+            error!("Unexpected error while parsing JSON: {}", e);
+            return None;
+        }
+    };
+    Some(map.as_object()?.get(hostname)?.as_str()?.to_owned())
+}
+
+/// Look up a machine ID on the configured libvirt VM hosts
+///
+/// This function iterates over the configured VM hosts and checks each one for
+/// a domain matching the specified hostname.  If no VM host is available or
+/// none of the configured hosts have a matching domain, `None` is returned.
+#[cfg(feature = "libvirt")]
+async fn from_libvirt(
+    hostname: &str,
+    config: Arc<Configuration>,
+) -> Option<String> {
+    let hostname = Arc::new(hostname.split('.').next().unwrap().to_string());
+    let res = task::spawn_blocking(move || {
+        for libvirt in &config.libvirt {
+            debug!("Checking {} for {}", libvirt.uri, hostname);
+            match libvirt::get_machine_id(&hostname, libvirt) {
+                Ok(v) => return Some(v),
+                Err(e) => {
+                    debug!("libvirt error: {}", e);
+                }
+            };
+        }
+        None
+    })
+    .await;
+    match res {
+        Ok(v) => v,
+        Err(e) => {
+            error!("Unexpected error while querying libvirt: {}", e);
+            None
+        }
+    }
+}
+
+/// Parse a UUID from a string
+///
+/// Returns `None` if the string does not contain a valid UUID.
+fn parse_uuid(value: &str) -> Option<Uuid> {
+    Uuid::parse_str(value).map_or_else(
+        |e| {
+            error!("Invalid UUID: {}", e);
+            None
+        },
+        Some,
+    )
+}

server/src/main.rs

@@ -0,0 +1,46 @@
+use std::path::PathBuf;
+
+use argh::FromArgs;
+use tracing_subscriber::EnvFilter;
+
+use sshca::config;
+use sshca::server;
+
+/// Online SSH CA Service
+#[derive(FromArgs)]
+struct Args {
+    /// path to configuration file
+    #[argh(option, short = 'c')]
+    config_file: Option<PathBuf>,
+
+    /// listen address
+    #[argh(option, short = 'l')]
+    listen_address: Option<String>,
+}
+
+#[tokio::main(flavor = "current_thread")]
+async fn main() {
+    tracing_subscriber::fmt()
+        .with_env_filter(EnvFilter::from_default_env())
+        .with_writer(std::io::stderr)
+        .init();
+
+    // stop libvirt printing to stderr
+    virt::error::clear_error_callback();
+
+    let args: Args = argh::from_env();
+
+    let listen_address = args
+        .listen_address
+        .as_ref()
+        .unwrap_or(&"[::]:8087".into())
+        .parse()
+        .unwrap();
+
+    let config = config::load_config(args.config_file.as_deref()).unwrap();
+    let app = server::make_app(config);
+    axum::Server::bind(&listen_address)
+        .serve(app.into_make_service())
+        .await
+        .unwrap();
+}

server/src/server/host.rs

@@ -0,0 +1,147 @@
+use std::collections::HashMap;
+use std::time::Duration;
+
+use axum::extract::multipart::{Multipart, MultipartError};
+use axum::extract::State;
+use axum::http::StatusCode;
+use axum::response::{IntoResponse, Response};
+use serde::Serialize;
+use ssh_key::Algorithm;
+use tracing::{debug, error, info, warn};
+
+use crate::auth::Claims;
+use crate::ca;
+
+#[derive(Serialize)]
+pub struct SignKeyResponse {
+    success: bool,
+    errors: Vec<String>,
+    certificates: HashMap<String, String>,
+}
+
+pub enum SignKeyError {
+    Multipart(MultipartError),
+    Cert(ca::CertError),
+    LoadPrivateKey(ca::LoadKeyError),
+    ParsePublicKey(ca::LoadKeyError),
+    UnsupportedAlgorithm(String),
+    NoKey,
+}
+
+impl From<MultipartError> for SignKeyError {
+    fn from(e: MultipartError) -> Self {
+        Self::Multipart(e)
+    }
+}
+
+impl From<ca::CertError> for SignKeyError {
+    fn from(e: ca::CertError) -> Self {
+        Self::Cert(e)
+    }
+}
+
+impl IntoResponse for SignKeyError {
+    fn into_response(self) -> Response {
+        match self {
+            Self::Multipart(e) => {
+                debug!("Error reading request: {}", e);
+                let body = e.to_string();
+                (StatusCode::BAD_REQUEST, body).into_response()
+            }
+            Self::Cert(e) => {
+                error!("Failed to sign certificate: {}", e);
+                let body = "Service Unavailable";
+                (StatusCode::SERVICE_UNAVAILABLE, body).into_response()
+            }
+            Self::LoadPrivateKey(e) => {
+                error!("Error loading CA private key: {}", e);
+                let body = "Service Unavailable";
+                (StatusCode::SERVICE_UNAVAILABLE, body).into_response()
+            }
+            Self::ParsePublicKey(e) => {
+                error!("Error parsing public keykey: {}", e);
+                let body = e.to_string();
+                (StatusCode::BAD_REQUEST, body).into_response()
+            }
+            Self::UnsupportedAlgorithm(a) => {
+                debug!("Requested certificate for unsupported key algorithm \"{}\"", a);
+                let body = format!("Unsupported key algorithm: {}", a);
+                (StatusCode::BAD_REQUEST, body).into_response()
+            }
+            Self::NoKey => {
+                debug!("No SSH public key provided in request");
+                (
+                    StatusCode::BAD_REQUEST,
+                    "No SSH public key provided in request",
+                )
+                    .into_response()
+            }
+        }
+    }
+}
+
+#[derive(Default)]
+struct SignKeyRequest {
+    hostname: String,
+    pubkey: Vec<u8>,
+    aliases: Vec<String>,
+}
+
+pub(super) async fn sign_host_cert(
+    claims: Claims,
+    State(ctx): State<super::State>,
+    mut form: Multipart,
+) -> Result<String, SignKeyError> {
+    let hostname = claims.sub;
+    let mut body = SignKeyRequest::default();
+
+    while let Some(field) = form.next_field().await? {
+        match field.name() {
+            Some("pubkey") => {
+                body.pubkey = field.bytes().await?.into();
+            }
+            Some("alias") => body.aliases.push(field.text().await?),
+            Some("hostname") => body.hostname = field.text().await?,
+            Some(n) => {
+                warn!("Client request included unsupported field {:?}", n);
+            }
+            None => {}
+        }
+    }
+    if body.pubkey.is_empty() {
+        return Err(SignKeyError::NoKey);
+    }
+    let aliases: Vec<_> = body.aliases.iter().map(String::as_ref).collect();
+
+    let config = &ctx.config;
+    let duration = Duration::from_secs(config.ca.host.cert_duration);
+    let privkey = ca::load_private_key(&config.ca.host.private_key_file)
+        .await
+        .map_err(SignKeyError::LoadPrivateKey)?;
+
+    let pubkey = ca::parse_public_key(&body.pubkey)
+        .map_err(SignKeyError::ParsePublicKey)?;
+    match pubkey.algorithm() {
+        Algorithm::Ecdsa { .. } => (),
+        Algorithm::Ed25519 => (),
+        Algorithm::Rsa { .. } => (),
+        _ => {
+            return Err(SignKeyError::UnsupportedAlgorithm(
+                pubkey.algorithm().as_str().into(),
+            ));
+        }
+    };
+    debug!(
+        "Signing {} key for {}",
+        pubkey.algorithm().as_str(),
+        hostname
+    );
+    let cert =
+        ca::sign_cert(&hostname, &pubkey, duration, &privkey, &aliases)?;
+    info!(
+        "Signed {} key for {}",
+        pubkey.algorithm().as_str(),
+        hostname
+    );
+    Ok(cert.to_openssh().map_err(ca::CertError::from)?)
+}

server/src/server/mod.rs

@@ -0,0 +1,110 @@
+mod host;
+
+use std::sync::Arc;
+
+use axum::async_trait;
+use axum::extract::FromRequestParts;
+use axum::headers::authorization::Bearer;
+use axum::headers::{Authorization, Host};
+use axum::http::request::Parts;
+use axum::http::StatusCode;
+use axum::response::{IntoResponse, Response};
+use axum::routing::{get, post};
+use axum::{RequestPartsExt, Router, TypedHeader};
+use tracing::debug;
+
+use crate::auth::{self, Claims};
+use crate::config::Configuration;
+use crate::machine_id;
+
+struct Context {
+    config: Arc<Configuration>,
+}
+
+type State = Arc<Context>;
+
+pub struct AuthError;
+
+impl IntoResponse for AuthError {
+    fn into_response(self) -> Response {
+        (StatusCode::UNAUTHORIZED, "Unauthorized").into_response()
+    }
+}
+
+#[async_trait]
+impl FromRequestParts<Arc<Context>> for Claims {
+    type Rejection = AuthError;
+
+    async fn from_request_parts(
+        parts: &mut Parts,
+        ctx: &State,
+    ) -> Result<Self, Self::Rejection> {
+        let TypedHeader(Authorization(bearer)) = parts
+            .extract::<TypedHeader<Authorization<Bearer>>>()
+            .await
+            .map_err(|e| {
+                debug!("Failed to extract token from HTTP request: {}", e);
+                AuthError
+            })?;
+        let host = parts.extract::<TypedHeader<Host>>().await.map_or_else(
+            |_| "localhost".to_owned(),
+            |v| v.hostname().to_owned(),
+        );
+
+        let hostname =
+            auth::get_token_subject(bearer.token()).map_err(|e| {
+                debug!("Could not get token subject: {}", e);
+                AuthError
+            })?;
+        let machine_id =
+            machine_id::get_machine_id(&hostname, ctx.config.clone())
+                .await
+                .ok_or_else(|| {
+                    debug!("No machine ID found for host {}", hostname);
+                    AuthError
+                })?;
+        let claims = auth::validate_token(
+            bearer.token(),
+            &hostname,
+            &machine_id,
+            &host,
+        )
+        .map_err(|e| {
+            debug!("Invalid auth token: {}", e);
+            AuthError
+        })?;
+        debug!("Successfully authenticated request from host {}", hostname);
+        Ok(claims)
+    }
+}
+
+pub fn make_app(config: Configuration) -> Router {
+    let ctx = Arc::new(Context {
+        config: config.into(),
+    });
+    Router::new()
+        .route("/", get(|| async { "UP" }))
+        .route("/host/sign", post(host::sign_host_cert))
+        .with_state(ctx)
+}
+
+#[cfg(test)]
+mod test {
+    use axum::body::Body;
+    use axum::http::Request;
+    use tower::ServiceExt;
+
+    use super::*;
+
+    #[tokio::test]
+    async fn test_up() {
+        let app = make_app(Configuration::default());
+        let response = app
+            .oneshot(Request::builder().uri("/").body(Body::empty()).unwrap())
+            .await
+            .unwrap();
+        assert_eq!(response.status(), StatusCode::OK);
+        let body = hyper::body::to_bytes(response.into_body()).await.unwrap();
+        assert_eq!(&body[..], b"UP");
+    }
+}

server/tests/common/mod.rs

@@ -0,0 +1,2 @@
+pub mod setup;
+pub mod token;

server/tests/common/setup.rs

@@ -0,0 +1,71 @@
+use std::error::Error;
+use std::io::prelude::*;
+use std::path::Path;
+use std::sync::Once;
+
+use rand_core::OsRng;
+use ssh_key::{Algorithm, Fingerprint, PrivateKey, PublicKey};
+use tempfile::NamedTempFile;
+use tracing_subscriber::EnvFilter;
+
+use sshca::config::Configuration;
+
+static INIT: Once = Once::new();
+
+fn gen_machine_ids() -> Result<NamedTempFile, Box<dyn Error>> {
+    let f = NamedTempFile::new()?;
+    let map = serde_json::json!({
+        "test.example.org": "b75e9126-d73a-4ae0-9a0d-63cb3552e6cd",
+    });
+    serde_json::to_writer(&f, &map)?;
+    Ok(f)
+}
+
+fn gen_config(machine_ids: &Path, host_key: &Path) -> Configuration {
+    let mut config = Configuration {
+        machine_ids: machine_ids.to_str().unwrap().into(),
+        ..Default::default()
+    };
+    config.ca.host.private_key_file = host_key.to_str().unwrap().into();
+    config
+}
+
+fn gen_ca_key() -> Result<(NamedTempFile, PublicKey), Box<dyn Error>> {
+    let key = PrivateKey::random(&mut OsRng, Algorithm::Ed25519)?;
+    let mut f = NamedTempFile::new()?;
+    f.write_all(key.to_openssh(Default::default())?.as_bytes())?;
+    Ok((f, key.public_key().clone()))
+}
+
+pub async fn setup() -> Result<(TestContext, Configuration), Box<dyn Error>> {
+    INIT.call_once(|| {
+        tracing_subscriber::fmt::fmt()
+            .with_env_filter(EnvFilter::from("sshca=trace"))
+            .with_test_writer()
+            .init();
+    });
+
+    let machine_ids = gen_machine_ids()?;
+    let (host_key, host_key_pub) = gen_ca_key()?;
+    let config = gen_config(machine_ids.path(), host_key.path());
+
+    let ctx = TestContext {
+        machine_ids,
+        host_key,
+        host_key_pub,
+    };
+    Ok((ctx, config))
+}
+
+#[allow(dead_code)]
+pub struct TestContext {
+    machine_ids: NamedTempFile,
+    host_key: NamedTempFile,
+    host_key_pub: PublicKey,
+}
+
+impl TestContext {
+    pub fn host_ca_fingerprint(&self) -> Fingerprint {
+        self.host_key_pub.fingerprint(Default::default())
+    }
+}

server/tests/common/token.rs

@@ -0,0 +1,41 @@
+use std::time;
+
+use argon2::Argon2;
+use jsonwebtoken::{encode, EncodingKey};
+use serde::Serialize;
+use uuid::Uuid;
+
+#[derive(Debug, Serialize)]
+struct TestClaims {
+    sub: String,
+    iss: String,
+    aud: String,
+    iat: u64,
+    nbf: u64,
+    exp: u64,
+}
+
+pub fn make_token(hostname: &str, machine_id: Uuid) -> String {
+    let now = time::SystemTime::now()
+        .duration_since(time::UNIX_EPOCH)
+        .unwrap()
+        .as_secs();
+    let claims = TestClaims {
+        sub: hostname.into(),
+        iss: hostname.into(),
+        aud: "sshca.example.org".into(),
+        nbf: now - 60,
+        iat: now,
+        exp: now + 60,
+    };
+    let mut secret = [0u8; 32];
+    Argon2::default()
+        .hash_password_into(
+            machine_id.as_bytes(),
+            hostname.as_bytes(),
+            &mut secret,
+        )
+        .unwrap();
+    let key = EncodingKey::from_secret(&secret);
+    encode(&Default::default(), &claims, &key).unwrap()
+}

server/tests/test_host.rs

@@ -0,0 +1,209 @@
+mod common;
+
+use axum::body::Body;
+use axum::http::{Request, StatusCode};
+use form_data_builder::FormData;
+use ssh_key::{Algorithm, Certificate};
+use tower::ServiceExt;
+use uuid::uuid;
+
+use sshca::server::make_app;
+
+use common::setup;
+use common::token;
+
+const ED25519_KEY: &str = concat!(
+    "ssh-ed25519 ",
+    "AAAAC3NzaC1lZDI1NTE5AAAAIAsFEmrNIoRHHUayEO0NdAIgtMvci/wME07h+A5XSNJy",
+);
+const DSA_KEY: &str = concat!(
+    "ssh-dss ",
+    "AAAAB3NzaC1kc3MAAACBALNAS+fZjaWt4q+MAgjf6HREFoYjgoSVJUUCtNmRGhND85msVtla",
+    "kll2gLzL6n6TWyiToARlThoTFu1ZDoGYauDL7iDXrGB6VWJEOQZ3TEMHLFYPziW02AbjR9GI",
+    "ptsF42D0bTTvvaIaBIhOTjWAUjuFIhAKhPkcj+udIcyH8CG1AAAAFQCpbXQSlxOvd4J92j2C",
+    "rWDYVGoK8wAAAIAfHiV6/glGZrDRztJmw1hfwbmiNPxaoSGkB+Necfkj0fZrlyLj8sLJIbGQ",
+    "w0dJMATZdRHw3Ql4R5IOu7sBfX1KQW++onT4ads/Xtl6vwfsjO2e/a6Y1ib9JCIOGJxNAAUC",
+    "JU0Fm0TSv2Nn6UTICAarp1eKALimqkvy1+ygBWjprgAAAIEAic5EpZH9wpgzvl9kPW531yrz",
+    "IOlCcXsJFPqQxUThrB2o1g3Rjpscd9kCw5UlPu6GGLk4aSN3UxeIKymTuKiEi7tvP1Tj/Bv5",
+    "tEc4rhfmrBAfAST09oRFDsELufsOAlTrJ0uk2LhtN14H1RBv9qPR5PQKTEYslyvXG1f8itNQ",
+    "YnQ="
+);
+
+fn make_test_request_body(key: &[u8], name: &str) -> (Body, String) {
+    let mut form = FormData::new(Vec::new());
+    form.write_file(
+        "pubkey",
+        key,
+        Some(name.as_ref()),
+        "application/octet-stream",
+    )
+    .unwrap();
+    let content_type = form.content_type_header();
+    let body = Body::from(form.finish().unwrap());
+    (body, content_type)
+}
+
+fn make_test_request(body: Body, content_type: &str) -> Request<Body> {
+    let hostname = "test.example.org";
+    let machine_id = uuid!("b75e9126-d73a-4ae0-9a0d-63cb3552e6cd");
+    let token = token::make_token(hostname, machine_id);
+    Request::builder()
+        .uri("/host/sign")
+        .method("POST")
+        .header("Authorization", format!("Bearer {}", token))
+        .header("Host", "sshca.example.org")
+        .header("Content-Type", content_type)
+        .body(body)
+        .unwrap()
+}
+
+#[tokio::test]
+async fn test_sign() {
+    let (ctx, config) = setup::setup().await.unwrap();
+
+    let app = make_app(config);
+    let (body, content_type) = make_test_request_body(
+        ED25519_KEY.as_bytes(),
+        "ssh_host_ed25519_key.pub",
+    );
+    let req = make_test_request(body, &content_type);
+    let res = app.oneshot(req).await.unwrap();
+
+    assert_eq!(res.status(), StatusCode::OK);
+    let body = hyper::body::to_bytes(res.into_body()).await.unwrap();
+    let cert = Certificate::from_openssh(std::str::from_utf8(&body).unwrap())
+        .unwrap();
+    assert_eq!(cert.algorithm(), Algorithm::Ed25519);
+    cert.validate(&[ctx.host_ca_fingerprint()]).unwrap();
+}
+
+#[tokio::test]
+async fn test_sign_invalid() {
+    let (_ctx, config) = setup::setup().await.unwrap();
+
+    let (body, content_type) = make_test_request_body(
+        "this is not a valid openssh key".as_bytes(),
+        "ssh_host_ecdsa_key.pub",
+    );
+    let app = make_app(config);
+    let req = make_test_request(body, &content_type);
+    let res = app.oneshot(req).await.unwrap();
+
+    assert_eq!(res.status(), StatusCode::BAD_REQUEST);
+    let body = hyper::body::to_bytes(res.into_body()).await.unwrap();
+    assert_eq!(
+        body,
+        concat!(
+            "Could not parse SSH key: ",
+            "Base64 encoding error: invalid Base64 encoding",
+        )
+    );
+}
+
+#[tokio::test]
+async fn test_sign_nokey() {
+    let (_ctx, config) = setup::setup().await.unwrap();
+
+    let mut form = FormData::new(Vec::new());
+    let content_type = form.content_type_header();
+    let body = Body::from(form.finish().unwrap());
+    let app = make_app(config);
+    let req = make_test_request(body, &content_type);
+    let res = app.oneshot(req).await.unwrap();
+
+    assert_eq!(res.status(), StatusCode::BAD_REQUEST);
+    let body = hyper::body::to_bytes(res.into_body()).await.unwrap();
+    assert_eq!(body, "No SSH public key provided in request",);
+}
+
+#[tokio::test]
+async fn test_sign_mangled() {
+    let (_ctx, config) = setup::setup().await.unwrap();
+
+    let app = make_app(config);
+    let mut form = FormData::new(Vec::new());
+    form.write_file(
+        "pubkey",
+        ED25519_KEY.as_bytes(),
+        Some("ssh_host_ed25519_key.pub".as_ref()),
+        "application/octet-stream",
+    )
+    .unwrap();
+    let content_type = form.content_type_header();
+    let mut form_bytes = form.finish().unwrap();
+    form_bytes.truncate(19);
+    let body = Body::from(form_bytes);
+    let req = make_test_request(body, &content_type);
+    let res = app.oneshot(req).await.unwrap();
+
+    assert_eq!(res.status(), StatusCode::BAD_REQUEST);
+    let body = hyper::body::to_bytes(res.into_body()).await.unwrap();
+    assert_eq!(body, "Error parsing `multipart/form-data` request",);
+}
+
+#[tokio::test]
+async fn test_sign_bad_request() {
+    let (_ctx, config) = setup::setup().await.unwrap();
+
+    let app = make_app(config);
+    let content_type = "text/plain";
+    let body = Body::from("test");
+    let req = make_test_request(body, content_type);
+    let res = app.oneshot(req).await.unwrap();
+
+    assert_eq!(res.status(), StatusCode::BAD_REQUEST);
+    let body = hyper::body::to_bytes(res.into_body()).await.unwrap();
+    assert_eq!(body, "Invalid `boundary` for `multipart/form-data` request",);
+}
+
+#[tokio::test]
+async fn test_sign_dsa() {
+    let (_ctx, config) = setup::setup().await.unwrap();
+
+    let app = make_app(config);
+    let (body, content_type) =
+        make_test_request_body(DSA_KEY.as_bytes(), "ssh_host_dsa_key.pub");
+    let req = make_test_request(body, &content_type);
+    let res = app.oneshot(req).await.unwrap();
+
+    assert_eq!(res.status(), StatusCode::BAD_REQUEST);
+    let body = hyper::body::to_bytes(res.into_body()).await.unwrap();
+    assert_eq!(body, "Unsupported key algorithm: ssh-dss");
+}
+
+#[tokio::test]
+async fn test_sign_failure() {
+    let (_ctx, mut config) = setup::setup().await.unwrap();
+    config.ca.host.private_key_file = "bogus".into();
+
+    let app = make_app(config);
+    let (body, content_type) = make_test_request_body(
+        ED25519_KEY.as_bytes(),
+        "ssh_host_ed25519_key.pub",
+    );
+    let req = make_test_request(body, &content_type);
+    let res = app.oneshot(req).await.unwrap();
+
+    assert_eq!(res.status(), StatusCode::SERVICE_UNAVAILABLE);
+    let body = hyper::body::to_bytes(res.into_body()).await.unwrap();
+    assert_eq!(body, "Service Unavailable");
+}
+
+#[tokio::test]
+async fn test_sign_unauthorized() {
+    // Deliberately drop the TestContext so the machine ID file gets deleted,
+    // which will cause authentication to fail.
+    let (_, config) = setup::setup().await.unwrap();
+
+    let app = make_app(config);
+    let (body, content_type) = make_test_request_body(
+        ED25519_KEY.as_bytes(),
+        "ssh_host_ed25519_key.pub",
+    );
+    let req = make_test_request(body, &content_type);
+    let res = app.oneshot(req).await.unwrap();
+
+    assert_eq!(res.status(), StatusCode::UNAUTHORIZED);
+    let body = hyper::body::to_bytes(res.into_body()).await.unwrap();
+    assert_eq!(body, "Unauthorized");
+}