[pbs-devel] [PATCH proxmox-ldap 2/6] add basic user auth functionality

[Lukas Wagner <l.wagner@proxmox.com>]

In the LDAP world, authentication is done using the bind operation, where
users are authenticated with the tuple (dn, password). Since we only know
the user's username, it is first necessary to look up the user's
domain (dn).

Signed-off-by: Lukas Wagner <l.wagner@proxmox.com>
---
 Cargo.toml |   5 ++
 src/lib.rs | 228 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 233 insertions(+)

diff --git a/Cargo.toml b/Cargo.toml
index 9caee04..021b14c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,3 +13,8 @@ homepage = "https://www.proxmox.com"
 exclude = [ "debian" ]
 
 [dependencies]
+anyhow = "1.0"
+ldap3 = { version = "0.11", default_features = false, features = ["tls"] }
+serde = { version = "1.0", features = ["derive"] }
+native-tls = "0.2"
+
diff --git a/src/lib.rs b/src/lib.rs
index e69de29..48eb863 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -0,0 +1,228 @@
+use std::{
+    fs,
+    path::{Path, PathBuf},
+    time::Duration,
+};
+
+use anyhow::{bail, Error};
+use ldap3::{
+    Ldap, LdapConnAsync, LdapConnSettings, LdapResult, Scope, SearchEntry,
+};
+use native_tls::{Certificate, TlsConnector, TlsConnectorBuilder};
+use serde::{Deserialize, Serialize};
+
+#[derive(PartialEq, Eq, Clone, Copy, Serialize, Deserialize, Debug)]
+/// LDAP connection security
+pub enum LdapConnectionMode {
+    /// unencrypted connection
+    Ldap,
+    /// upgrade to TLS via STARTTLS
+    StartTls,
+    /// TLS via LDAPS
+    Ldaps,
+}
+
+#[derive(Clone, Serialize, Deserialize)]
+/// Configuration for LDAP connections
+pub struct LdapConfig {
+    /// Array of servers that will be tried in order
+    pub servers: Vec<String>,
+    /// Port
+    pub port: Option<u16>,
+    /// LDAP attribute containing the user id. Will be used to look up the user's domain
+    pub user_attr: String,
+    /// LDAP base domain
+    pub base_dn: String,
+    /// LDAP bind domain, will be used for user lookup/sync if set
+    pub bind_dn: Option<String>,
+    /// LDAP bind password, will be used for user lookup/sync if set
+    pub bind_password: Option<String>,
+    /// Connection security
+    pub tls_mode: LdapConnectionMode,
+    /// Verify the server's TLS certificate
+    pub verify_certificate: bool,
+    /// Root certificates that should be trusted, in addition to
+    /// the ones from the certificate store.
+    /// Expects X.509 certs in PEM format.
+    pub additional_trusted_certificates: Option<Vec<PathBuf>>,
+    /// Override the path to the system's default certificate store
+    /// in /etc/ssl/certs (added for PVE compatibility)
+    pub certificate_store_path: Option<PathBuf>,
+}
+
+/// Connection to an LDAP server, can be used to authenticate users.
+pub struct LdapConnection {
+    /// Configuration for this connection
+    config: LdapConfig,
+}
+
+impl LdapConnection {
+    /// Default port for LDAP/StartTls connections
+    const LDAP_DEFAULT_PORT: u16 = 389;
+    /// Default port for LDAPS connections
+    const LDAPS_DEFAULT_PORT: u16 = 636;
+    /// Connection timeout
+    const LDAP_CONNECTION_TIMEOUT: Duration = Duration::from_secs(5);
+
+    /// Create a new LDAP connection.
+    pub fn new(config: LdapConfig) -> Self {
+        Self { config }
+    }
+
+    /// Authenticate a user with username/password.
+    ///
+    /// The user's domain is queried is by performing an LDAP search with the configured bind_dn
+    /// and bind_password. If no bind_dn is provided, an anonymous search is attempted.
+    pub async fn authenticate_user(&self, username: &str, password: &str) -> Result<(), Error> {
+        let user_dn = self.search_user_dn(username).await?;
+
+        let mut ldap = self.create_connection().await?;
+
+        // Perform actual user authentication by binding.
+        let _: LdapResult = ldap.simple_bind(&user_dn, password).await?.success()?;
+
+        // We are already authenticated, so don't fail if terminating the connection
+        // does not work for some reason.
+        let _: Result<(), _> = ldap.unbind().await;
+
+        Ok(())
+    }
+
+    /// Retrive port from LDAP configuration, otherwise use the correct default
+    fn port_from_config(&self) -> u16 {
+        self.config.port.unwrap_or_else(|| {
+            if self.config.tls_mode == LdapConnectionMode::Ldaps {
+                Self::LDAPS_DEFAULT_PORT
+            } else {
+                Self::LDAP_DEFAULT_PORT
+            }
+        })
+    }
+
+    /// Determine correct URL scheme from LDAP config
+    fn scheme_from_config(&self) -> &'static str {
+        if self.config.tls_mode == LdapConnectionMode::Ldaps {
+            "ldaps"
+        } else {
+            "ldap"
+        }
+    }
+
+    /// Construct URL from LDAP config
+    fn ldap_url_from_config(&self, server: &str) -> String {
+        let port = self.port_from_config();
+        let scheme = self.scheme_from_config();
+        format!("{scheme}://{server}:{port}")
+    }
+
+    fn add_cert_to_builder<P: AsRef<Path>>(
+        path: P,
+        builder: &mut TlsConnectorBuilder,
+    ) -> Result<(), Error> {
+        let bytes = fs::read(path)?;
+        let cert = Certificate::from_pem(&bytes)?;
+        builder.add_root_certificate(cert);
+
+        Ok(())
+    }
+
+    async fn try_connect(&self, url: &str) -> Result<(LdapConnAsync, Ldap), Error> {
+        let starttls = self.config.tls_mode == LdapConnectionMode::StartTls;
+
+        let mut builder = TlsConnector::builder();
+        builder.danger_accept_invalid_certs(!self.config.verify_certificate);
+
+        if let Some(certificate_paths) = self.config.additional_trusted_certificates.as_deref() {
+            for path in certificate_paths {
+                Self::add_cert_to_builder(path, &mut builder)?;
+            }
+        }
+
+        if let Some(certificate_store_path) = self.config.certificate_store_path.as_deref() {
+            builder.disable_built_in_roots(true);
+
+            for dir_entry in fs::read_dir(certificate_store_path)? {
+                let dir_entry = dir_entry?;
+
+                if !dir_entry.metadata()?.is_dir() {
+                    Self::add_cert_to_builder(dir_entry.path(), &mut builder)?;
+                }
+            }
+        }
+
+        LdapConnAsync::with_settings(
+            LdapConnSettings::new()
+                .set_starttls(starttls)
+                .set_conn_timeout(Self::LDAP_CONNECTION_TIMEOUT)
+                .set_connector(builder.build()?),
+            url,
+        )
+        .await
+        .map_err(|e| e.into())
+    }
+
+    /// Create LDAP connection
+    ///
+    /// If a connection to the server cannot be established, the fallbacks
+    /// are tried.
+    async fn create_connection(&self) -> Result<Ldap, Error> {
+        let mut last_error = None;
+
+        for server in &self.config.servers {
+            match self.try_connect(&self.ldap_url_from_config(server)).await {
+                Ok((connection, ldap)) => {
+                    ldap3::drive!(connection);
+                    return Ok(ldap);
+                }
+                Err(e) => {
+                    last_error = Some(e);
+                }
+            }
+        }
+
+        Err(last_error.unwrap())
+    }
+
+    /// Search a user's domain.
+    async fn search_user_dn(&self, username: &str) -> Result<String, Error> {
+        let mut ldap = self.create_connection().await?;
+
+        if let Some(bind_dn) = self.config.bind_dn.as_deref() {
+            let password = self.config.bind_password.as_deref().unwrap_or_default();
+            let _: LdapResult = ldap.simple_bind(bind_dn, password).await?.success()?;
+
+            let user_dn = self.do_search_user_dn(username, &mut ldap).await;
+
+            ldap.unbind().await?;
+
+            user_dn
+        } else {
+            self.do_search_user_dn(username, &mut ldap).await
+        }
+    }
+
+    async fn do_search_user_dn(&self, username: &str, ldap: &mut Ldap) -> Result<String, Error> {
+        let query = format!("(&({}={}))", self.config.user_attr, username);
+
+        let (entries, _res) = ldap
+            .search(&self.config.base_dn, Scope::Subtree, &query, vec!["dn"])
+            .await?
+            .success()?;
+
+        if entries.len() > 1 {
+            bail!(
+                "found multiple users with attribute `{}={}`",
+                self.config.user_attr,
+                username
+            )
+        }
+
+        if let Some(entry) = entries.into_iter().next() {
+            let entry = SearchEntry::construct(entry);
+
+            return Ok(entry.dn);
+        }
+
+        bail!("user not found")
+    }
+}
-- 
2.30.2