diff --git a/src/auth.rs b/src/auth.rs
index 870e19a..5c78083 100644
--- a/src/auth.rs
+++ b/src/auth.rs
@@ -15,12 +15,17 @@ use tokio::sync::Mutex;
 use tracing::{event, instrument, Level};
 
 use crate::{
+    config::AuthBackendConfig,
     db::{/* Database, */ Database, SqliteDatabase, UserTokenEntry},
     secrets::{
         PadlockGenerationSecret, Password, ServerHash, ServerPadlock, UserServerKey, UserToken,
     },
 };
 
+use self::backends::{LdapBackend, ValidateLogin};
+
+pub mod backends;
+
 #[derive(Debug, Error)]
 pub enum AuthenticationError {
     #[error("Invalid username or password")]
@@ -31,18 +36,48 @@ pub enum AuthenticationError {
     InvalidServerHash,
     #[error("Database error")]
     Database(#[from] sqlx::Error),
+    #[error("Authentication backend error")]
+    Backend(#[from] ldap3::LdapError),
+    #[error("No authentication backends available")]
+    NoBackends,
+}
+
+#[derive(Debug)]
+pub enum AuthenticationBackend {
+    Ldap(Arc<LdapBackend>),
+}
+
+impl AuthenticationBackend {
+    pub async fn new(config: AuthBackendConfig) -> Result<Self, AuthenticationError> {
+        match config {
+            AuthBackendConfig::Ldap(c) => Ok(Self::Ldap(LdapBackend::new(c).await?)),
+        }
+    }
+}
+
+impl ValidateLogin for AuthenticationBackend {
+    async fn validate_login(
+        &self,
+        username: &str,
+        password: &Password,
+    ) -> Result<String, AuthenticationError> {
+        match self {
+            AuthenticationBackend::Ldap(b) => b.validate_login(username, password).await,
+        }
+    }
 }
 
 #[derive(Debug)]
 pub struct UserAuthenticator {
     db: Arc<Mutex<SqliteDatabase>>,
+    backends: Vec<AuthenticationBackend>,
 }
 
 impl UserAuthenticator {
     const TOKEN_LEN: usize = 30;
 
-    pub fn new(db: Arc<Mutex<SqliteDatabase>>) -> Self {
-        Self { db }
+    pub fn new(db: Arc<Mutex<SqliteDatabase>>, backends: Vec<AuthenticationBackend>) -> Self {
+        Self { db, backends }
     }
 
     #[instrument]
@@ -50,16 +85,33 @@ impl UserAuthenticator {
         &self,
         username: &str,
         password: &Password,
-    ) -> Result<UserToken, AuthenticationError> {
-        // TODO: validate password
+    ) -> Result<(String, UserToken), AuthenticationError> {
+        let mut auth_result = Err(AuthenticationError::NoBackends);
+
+        for backend in &self.backends {
+            auth_result = backend.validate_login(username, password).await;
+            match &auth_result {
+                Ok(_) => {
+                    break;
+                }
+                Err(err) => {
+                    event!(Level::WARN, ?err, "Authentication with backend failed");
+                }
+            }
+        }
+
+        let Ok(username) = auth_result else {
+            event!(Level::WARN, "Authentication failed with all backends");
+            return Err(AuthenticationError::InvalidUserOrPassword);
+        };
 
         let new_token =
             UserToken::from(Alphanumeric.sample_string(&mut thread_rng(), Self::TOKEN_LEN));
 
         let mut db = self.db.lock().await;
-        db.save_token(username, &new_token).await?;
+        db.save_token(&username, &new_token).await?;
 
-        Ok(new_token)
+        Ok((username, new_token))
     }
 
     #[instrument]
diff --git a/src/auth/backends.rs b/src/auth/backends.rs
new file mode 100644
index 0000000..4c1b3b6
--- /dev/null
+++ b/src/auth/backends.rs
@@ -0,0 +1,176 @@
+use std::{cmp::min, convert::Infallible, sync::Arc, time::Duration};
+
+use ldap3::{drive, ldap_escape, Ldap, LdapConnAsync, LdapError, Scope, SearchEntry};
+use secrecy::ExposeSecret;
+use tokio::{sync::Mutex, time::sleep};
+use tracing::{event, instrument, Level};
+
+use crate::{config::LdapBackendConfig, secrets::Password};
+
+use super::AuthenticationError;
+
+pub trait ValidateLogin {
+    /// Validates that the given username and password combination is correct, and returns the
+    /// (normalized) user ID.
+    async fn validate_login(
+        &self,
+        username: &str,
+        password: &Password,
+    ) -> Result<String, AuthenticationError>;
+}
+
+#[instrument]
+async fn start_ldap_connection(
+    config: &LdapBackendConfig,
+) -> Result<(LdapConnAsync, Ldap), LdapError> {
+    event!(Level::INFO, "Opening LDAP connection");
+
+    LdapConnAsync::new(&config.server_address).await
+}
+
+#[derive(Debug)]
+pub struct LdapBackend {
+    ldap: Arc<Mutex<Ldap>>,
+    config: LdapBackendConfig,
+}
+
+impl LdapBackend {
+    #[instrument]
+    pub async fn new(config: LdapBackendConfig) -> Result<Arc<Self>, LdapError> {
+        let (conn, ldap) = start_ldap_connection(&config).await?;
+        let ldap = Arc::new(Mutex::new(ldap));
+
+        let this = Arc::new(Self { ldap, config });
+
+        {
+            let this = Arc::clone(&this);
+            tokio::spawn(async move { this.drive_and_restart_connection(conn).await });
+        }
+
+        Ok(this)
+    }
+
+    #[instrument(skip(conn))]
+    async fn drive_and_restart_connection(&self, conn: LdapConnAsync) -> Infallible {
+        const MAX_RECONNECT_DELAY: Duration = Duration::from_secs(60);
+
+        let mut conn = conn;
+
+        loop {
+            let ret = conn.drive().await;
+            match ret {
+                Ok(()) => event!(
+                    Level::ERROR,
+                    "LDAP connection exited without specific error"
+                ),
+                Err(err) => event!(Level::ERROR, ?err, "LDAP connection exited"),
+            }
+
+            // try to get a new connection
+            let mut delay = Duration::from_secs(1);
+            let (new_conn, ldap) = loop {
+                match start_ldap_connection(&self.config).await {
+                    Ok(ret) => {
+                        event!(Level::INFO, "Successfully reconnected");
+                        break ret;
+                    }
+                    Err(err) => {
+                        event!(
+                            Level::WARN,
+                            ?err,
+                            "Reconnecting to LDAP failed, reconnecting in {}s",
+                            delay.as_secs()
+                        );
+                        sleep(delay).await;
+                        delay = min(delay * 2, MAX_RECONNECT_DELAY);
+                    }
+                }
+            };
+
+            conn = new_conn;
+            *self.ldap.lock().await = ldap;
+        }
+    }
+}
+
+impl ValidateLogin for LdapBackend {
+    #[instrument]
+    async fn validate_login(
+        &self,
+        username: &str,
+        password: &Password,
+    ) -> Result<String, AuthenticationError> {
+        let filter = self
+            .config
+            .user_filter
+            .replace("%s", &ldap_escape(username));
+
+        event!(Level::DEBUG, filter, "Validating LDAP user");
+
+        let search_results = self
+            .ldap
+            .lock()
+            .await
+            .search(
+                &self.config.search_base,
+                Scope::Subtree,
+                &filter,
+                ["dn", "uid"],
+            )
+            .await?
+            .success()?
+            .0;
+
+        event!(Level::TRACE, ?search_results, "Got raw search results");
+
+        let search_entry = match search_results.len() {
+            1 => SearchEntry::construct(search_results.into_iter().next().unwrap()),
+            0 => {
+                event!(Level::WARN, "No matching LDAP user found");
+                return Err(AuthenticationError::InvalidUserOrPassword);
+            }
+            _ => {
+                event!(Level::ERROR, "Multiple LDAP users matched");
+                return Err(AuthenticationError::InvalidUserOrPassword);
+            }
+        };
+
+        let uid = {
+            let uids = search_entry.attrs.get("uid").ok_or_else(|| {
+                event!(
+                    Level::ERROR,
+                    "LDAP entry doesn't contain a uid attr, rejecting"
+                );
+                AuthenticationError::InvalidUserOrPassword
+            })?;
+
+            if uids.len() != 1 {
+                event!(
+                    Level::ERROR,
+                    ?uids,
+                    "LDAP entry contains multiple uid attrs"
+                );
+                return Err(AuthenticationError::InvalidUserOrPassword);
+            }
+
+            uids[0].clone()
+        };
+
+        event!(
+            Level::TRACE,
+            dn = search_entry.dn,
+            uid,
+            "Found LDAP user, attempting to bind"
+        );
+
+        // try to bind as the found user
+        {
+            let (conn, mut ldap) = start_ldap_connection(&self.config).await?;
+            drive!(conn);
+            ldap.simple_bind(&search_entry.dn, password.0.expose_secret())
+                .await?;
+        }
+
+        Ok(uid)
+    }
+}
diff --git a/src/config.rs b/src/config.rs
index 086bec9..2ae370d 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -31,4 +31,7 @@ pub enum AuthBackendConfig {
 #[serde(rename_all = "kebab-case")]
 pub struct LdapBackendConfig {
     pub server_address: String,
+    pub search_base: String,
+    /// User filter template. All occurences of `%s` will be replaced with the username.
+    pub user_filter: String,
 }
diff --git a/src/main.rs b/src/main.rs
index c84cb0e..517f82c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -27,7 +27,9 @@ mod server;
 
 use std::sync::Arc;
 
-use auth::{ServerPadlockGenerator, UserAuthenticator, UserServerKeyGenerator};
+use auth::{
+    AuthenticationBackend, ServerPadlockGenerator, UserAuthenticator, UserServerKeyGenerator,
+};
 use clap::Parser;
 use color_eyre::Result;
 use config::Config;
@@ -84,7 +86,12 @@ async fn main() -> Result<()> {
         SqliteDatabase::open(&config.database.connection_string).await,
     ));
 
-    let user_authenticator = Arc::new(UserAuthenticator::new(database));
+    let mut auth_backends = vec![];
+    for c in config.auth_backends {
+        auth_backends.push(AuthenticationBackend::new(c).await?);
+    }
+
+    let user_authenticator = Arc::new(UserAuthenticator::new(database, auth_backends));
     let padlock_generator = Arc::new(ServerPadlockGenerator::new(config.padlock_secret));
     let user_server_key_generator = Arc::new(UserServerKeyGenerator::new(
         Arc::clone(&user_authenticator),
diff --git a/src/server.rs b/src/server.rs
index 5379686..b650c57 100644
--- a/src/server.rs
+++ b/src/server.rs
@@ -109,7 +109,7 @@ async fn api_login(
 ) -> ApiResult<Json<LoginResponse>> {
     event!(Level::INFO, "Generating user key");
 
-    let user_token = state
+    let (username, user_token) = state
         .user_authenticator
         .create_user_token(&username, &password)
         .await?;