diff --git a/src/grpc.rs b/src/grpc.rs
index 3dd2c21..5c20ae2 100644
--- a/src/grpc.rs
+++ b/src/grpc.rs
@@ -8,6 +8,7 @@ use std::{
     },
 };
 
+use axum_extra::extract::cookie::Key;
 use defguard_version::{
     get_tracing_variables,
     server::{grpc::DefguardVersionInterceptor, DefguardVersionLayer},
@@ -31,6 +32,7 @@ use crate::{
 
 // connected clients
 type ClientMap = HashMap<SocketAddr, mpsc::UnboundedSender<Result<CoreRequest, Status>>>;
+static COOKIE_KEY_HEADER: &str = "dg-cookie-key-bin";
 
 #[derive(Debug, Clone, Default)]
 pub(crate) struct Configuration {
@@ -42,6 +44,7 @@ pub(crate) struct ProxyServer {
     current_id: Arc<AtomicU64>,
     clients: Arc<Mutex<ClientMap>>,
     results: Arc<Mutex<HashMap<u64, oneshot::Sender<core_response::Payload>>>>,
+    http_channel: mpsc::UnboundedSender<Key>,
     pub(crate) connected: Arc<AtomicBool>,
     pub(crate) core_version: Arc<Mutex<Option<Version>>>,
     config: Arc<Mutex<Option<Configuration>>>,
@@ -51,8 +54,9 @@ pub(crate) struct ProxyServer {
 impl ProxyServer {
     #[must_use]
     /// Create new `ProxyServer`.
-    pub(crate) fn new() -> Self {
+    pub(crate) fn new(http_channel: mpsc::UnboundedSender<Key>) -> Self {
         Self {
+            http_channel,
             current_id: Arc::new(AtomicU64::new(1)),
             clients: Arc::new(Mutex::new(HashMap::new())),
             results: Arc::new(Mutex::new(HashMap::new())),
@@ -189,6 +193,7 @@ impl Clone for ProxyServer {
             results: Arc::clone(&self.results),
             connected: Arc::clone(&self.connected),
             core_version: Arc::clone(&self.core_version),
+            http_channel: self.http_channel.clone(),
             config: Arc::clone(&self.config),
             setup_in_progress: Arc::clone(&self.setup_in_progress),
         }
@@ -228,6 +233,30 @@ impl proxy_server::Proxy for ProxyServer {
 
         info!("Defguard Core gRPC client connected from: {address}");
 
+        // Retrieve private cookies key from the header.
+        let cookie_key = request.metadata().get_bin(COOKIE_KEY_HEADER);
+        let key = match cookie_key {
+            Some(key) => Key::from(&key.to_bytes().map_err(|err| {
+                error!("Failed to decode private cookie key: {err:?}");
+                Status::internal("Failed to decode private cookie key")
+            })?),
+            // If the header is missing, fall back to generating a local key.
+            // This preserves compatibility with older Core versions that did not
+            // provide a shared cookie key. In this mode, cookie-based sessions will
+            // not be shared across proxy instances and HA won't work.
+            None => {
+                warn!(
+                    "Private cookie key not provided by Core; falling back to a locally generated key. \
+                     This typically indicates an older Core version and disables cookie sharing across proxies."
+                );
+                Key::generate()
+            }
+        };
+        self.http_channel.send(key).map_err(|err| {
+            error!("Failed to send private cookies key to HTTP server: {err:?}");
+            Status::internal("Failed to send private cookies key to HTTP server")
+        })?;
+
         let (tx, rx) = mpsc::unbounded_channel();
         self.clients
             .lock()
diff --git a/src/http.rs b/src/http.rs
index f18d52d..56ee352 100644
--- a/src/http.rs
+++ b/src/http.rs
@@ -22,7 +22,7 @@ use defguard_version::{server::DefguardVersionLayer, Version};
 use serde::Serialize;
 use tokio::{
     net::TcpListener,
-    sync::{oneshot, Mutex},
+    sync::{mpsc, oneshot, Mutex},
     task::JoinSet,
 };
 use tower_governor::{
@@ -178,18 +178,13 @@ pub async fn run_server(config: Config) -> anyhow::Result<()> {
     debug!("Using config: {config:?}");
 
     let mut tasks = JoinSet::new();
-    // connect to upstream gRPC server
-    let grpc_server = ProxyServer::new();
 
-    // build application
-    debug!("Setting up API server");
-    let shared_state = AppState {
-        grpc_server: grpc_server.clone(),
-        remote_mfa_sessions: Arc::new(tokio::sync::Mutex::new(HashMap::new())),
-        // Generate secret key for encrypting cookies.
-        key: Key::generate(),
-        url: config.url.clone(),
-    };
+    // Prepare the channel for gRPC -> http server communication.
+    // The channel sends private cookies key once core connects to gRPC.
+    let (tx, mut rx) = mpsc::unbounded_channel::<Key>();
+
+    // connect to upstream gRPC server
+    let grpc_server = ProxyServer::new(tx);
 
     let server_clone = grpc_server.clone();
 
@@ -261,6 +256,20 @@ pub async fn run_server(config: Config) -> anyhow::Result<()> {
         }
     });
 
+    // Wait for core to connect to gRPC and send private cookies encryption key.
+    let Some(key) = rx.recv().await else {
+        return Err(anyhow::Error::msg("http channel closed"));
+    };
+
+    // build application
+    debug!("Setting up API server");
+    let shared_state = AppState {
+        key,
+        grpc_server: grpc_server,
+        remote_mfa_sessions: Arc::new(tokio::sync::Mutex::new(HashMap::new())),
+        url: config.url.clone(),
+    };
+
     // Setup tower_governor rate-limiter
     debug!(
         "Configuring rate limiter, per_second: {}, burst: {}",