ldap: add method for retrieving root DSE attributes

The root DSE holds common attributes about the LDAP server itself.
Needed to e.g. support Active Directory-based LDAP servers to retrieve
the base DN from the server itself, based on an valid bind.

See also RFC 4512, Section 5.1 [0] for more information about this
special object.

[0] https://www.rfc-editor.org/rfc/rfc4512#section-5.1

Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>

proxmox-ldap/src/lib.rs

@@ -193,6 +193,28 @@ impl Connection {
         Ok(())
     }
 
+    /// Retrieves an attribute from the root DSE according to RFC 4512, Section 5.1
+    /// https://www.rfc-editor.org/rfc/rfc4512#section-5.1
+    pub async fn retrieve_root_dse_attr(&self, attr: &str) -> Result<Vec<String>, Error> {
+        let mut ldap = self.create_connection().await?;
+
+        let (entries, _res) = ldap
+            .search("", Scope::Base, "(objectClass=*)", &[attr])
+            .await?
+            .success()?;
+
+        if entries.len() > 1 {
+            bail!("found multiple root DSEs with attribute '{attr}'");
+        }
+
+        entries
+            .into_iter()
+            .next()
+            .map(SearchEntry::construct)
+            .and_then(|e| e.attrs.get(attr).cloned())
+            .ok_or_else(|| format_err!("failed to retrieve root DSE attribute '{attr}'"))
+    }
+
     /// Retrive port from LDAP configuration, otherwise use the correct default
     fn port_from_config(&self) -> u16 {
         self.config.port.unwrap_or_else(|| {

proxmox-ldap/tests/assets/glauth.cfg

@@ -16,6 +16,7 @@ debug = true
   baseDN = "dc=example,dc=com"
   nameformat = "cn"
   groupformat = "ou"
+  anonymousdse = true
 
 # to create a passSHA256:   echo -n "mysecret" | openssl dgst -sha256
 

proxmox-ldap/tests/glauth.rs

@@ -191,3 +191,19 @@ fn test_check_connection() -> Result<(), Error> {
 
     Ok(())
 }
+
+#[test]
+#[ignore]
+fn test_retrieve_root_dse_attr() -> Result<(), Error> {
+    let _glauth = GlauthServer::new("tests/assets/glauth.cfg")?;
+
+    let connection = Connection::new(default_config());
+
+    let values = proxmox_async::runtime::block_on(
+        connection.retrieve_root_dse_attr("defaultNamingContext"),
+    )?;
+
+    assert_eq!(values, vec!["dc=example,dc=com"]);
+
+    Ok(())
+}