diff --git a/README.md b/README.md
index f61fefe19..6d53769d2 100644
--- a/README.md
+++ b/README.md
@@ -20,12 +20,16 @@ immediately, without going through the acceptance testing process of our quality
 
 ### From sources
 
-Ensure that you have [the Rust toolchain installed][install_rust], then clone this repository and run:
+Ensure that you have [the Rust toolchain installed][install_rust] and [libsodium][libsodium] installed on your system, then clone this repository and run:
 
 ```shell
 cargo install --path ./devolutions-gateway
 ```
 
+> **Note:** `libsodium` is required as a native dependency for in-memory credential protection.
+> On Windows, it is vendored automatically via vcpkg.
+> On Linux and macOS, install it using your system package manager (e.g., `apt install libsodium-dev` or `brew install libsodium`).
+
 ## Configuration
 
 Devolutions Gateway is configured using a JSON document.
@@ -339,6 +343,7 @@ See the dedicated [README.md file](./.github/workflows/README.md) in the `workfl
 [official_website]: https://devolutions.net/gateway/download/
 [github_release]: https://github.com/Devolutions/devolutions-gateway/releases
 [install_rust]: https://www.rust-lang.org/tools/install
+[libsodium]: https://libsodium.org/
 [psmodule]: https://www.powershellgallery.com/packages/DevolutionsGateway/
 [rustls]: https://crates.io/crates/rustls
 [microsoft_tls]: https://learn.microsoft.com/en-us/windows-server/security/tls/tls-registry-settings
diff --git a/devolutions-gateway/src/api/preflight.rs b/devolutions-gateway/src/api/preflight.rs
index afa2e1eea..24929b5f1 100644
--- a/devolutions-gateway/src/api/preflight.rs
+++ b/devolutions-gateway/src/api/preflight.rs
@@ -11,7 +11,7 @@ use uuid::Uuid;
 
 use crate::DgwState;
 use crate::config::Conf;
-use crate::credential::CredentialStoreHandle;
+use crate::credential::{CredentialStoreHandle, InsertError};
 use crate::extract::PreflightScope;
 use crate::http::HttpError;
 use crate::session::SessionMessageSender;
@@ -340,7 +340,14 @@ async fn handle_operation(
             let previous_entry = credential_store
                 .insert(token, mapping, time_to_live)
                 .inspect_err(|error| warn!(%operation.id, error = format!("{error:#}"), "Failed to insert credentials"))
-                .map_err(|e| PreflightError::new(PreflightAlertStatus::InternalServerError, format!("{e:#}")))?;
+                .map_err(|e| match e {
+                    InsertError::InvalidToken(_) => {
+                        PreflightError::new(PreflightAlertStatus::InvalidParams, format!("{e:#}"))
+                    }
+                    InsertError::Internal(_) => {
+                        PreflightError::new(PreflightAlertStatus::InternalServerError, format!("{e:#}"))
+                    }
+                })?;
 
             if previous_entry.is_some() {
                 outputs.push(PreflightOutput {
diff --git a/devolutions-gateway/src/credential/mod.rs b/devolutions-gateway/src/credential/mod.rs
index 9bd1114da..792e8bb1e 100644
--- a/devolutions-gateway/src/credential/mod.rs
+++ b/devolutions-gateway/src/credential/mod.rs
@@ -4,6 +4,7 @@ mod crypto;
 pub use crypto::{DecryptedPassword, EncryptedPassword};
 
 use std::collections::HashMap;
+use std::fmt;
 use std::sync::Arc;
 
 use anyhow::Context;
@@ -15,6 +16,28 @@ use uuid::Uuid;
 
 use self::crypto::MASTER_KEY;
 
+/// Error returned by [`CredentialStoreHandle::insert`].
+#[derive(Debug)]
+pub enum InsertError {
+    /// The provided token is invalid (e.g., missing or malformed JTI).
+    ///
+    /// This is a client-side error: the caller supplied bad input.
+    InvalidToken(anyhow::Error),
+    /// An internal error occurred (e.g., encryption failure).
+    Internal(anyhow::Error),
+}
+
+impl fmt::Display for InsertError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::InvalidToken(e) => e.fmt(f),
+            Self::Internal(e) => e.fmt(f),
+        }
+    }
+}
+
+impl std::error::Error for InsertError {}
+
 /// Credential at the application protocol level
 #[derive(Debug, Clone)]
 pub enum AppCredential {
@@ -112,8 +135,11 @@ impl CredentialStoreHandle {
         token: String,
         mapping: Option<CleartextAppCredentialMapping>,
         time_to_live: time::Duration,
-    ) -> anyhow::Result<Option<ArcCredentialEntry>> {
-        let mapping = mapping.map(CleartextAppCredentialMapping::encrypt).transpose()?;
+    ) -> Result<Option<ArcCredentialEntry>, InsertError> {
+        let mapping = mapping
+            .map(CleartextAppCredentialMapping::encrypt)
+            .transpose()
+            .map_err(InsertError::Internal)?;
         self.0.lock().insert(token, mapping, time_to_live)
     }
 
@@ -148,8 +174,10 @@ impl CredentialStore {
         token: String,
         mapping: Option<AppCredentialMapping>,
         time_to_live: time::Duration,
-    ) -> anyhow::Result<Option<ArcCredentialEntry>> {
-        let jti = crate::token::extract_jti(&token).context("failed to extract token ID")?;
+    ) -> Result<Option<ArcCredentialEntry>, InsertError> {
+        let jti = crate::token::extract_jti(&token)
+            .context("failed to extract token ID")
+            .map_err(InsertError::InvalidToken)?;
 
         let entry = CredentialEntry {
             token,
diff --git a/devolutions-gateway/src/rd_clean_path.rs b/devolutions-gateway/src/rd_clean_path.rs
index 10ff4cd5b..6d4614b5e 100644
--- a/devolutions-gateway/src/rd_clean_path.rs
+++ b/devolutions-gateway/src/rd_clean_path.rs
@@ -4,9 +4,9 @@ use std::sync::Arc;
 
 use anyhow::Context as _;
 use ironrdp_connector::sspi;
-use secrecy::ExposeSecret as _;
 use ironrdp_pdu::nego;
 use ironrdp_rdcleanpath::RDCleanPathPdu;
+use secrecy::ExposeSecret as _;
 use tap::prelude::*;
 use thiserror::Error;
 use tokio::io::{AsyncRead, AsyncReadExt as _, AsyncWrite, AsyncWriteExt as _};
@@ -405,7 +405,11 @@ async fn handle_with_credential_injection(
             } = user;
 
             // The username is in the FQDN format. Thus, the domain field can be empty.
-            sspi::CredentialsBuffers::AuthIdentity(sspi::AuthIdentityBuffers::from_utf8(fqdn, "", password.expose_secret()))
+            sspi::CredentialsBuffers::AuthIdentity(sspi::AuthIdentityBuffers::from_utf8(
+                fqdn,
+                "",
+                password.expose_secret(),
+            ))
         });
 
         Some(sspi::KerberosServerConfig {
diff --git a/devolutions-gateway/src/rdp_proxy.rs b/devolutions-gateway/src/rdp_proxy.rs
index c8cfda6ea..b3dc466a7 100644
--- a/devolutions-gateway/src/rdp_proxy.rs
+++ b/devolutions-gateway/src/rdp_proxy.rs
@@ -3,11 +3,11 @@ use std::sync::Arc;
 
 use anyhow::Context as _;
 use ironrdp_acceptor::credssp::CredsspProcessGenerator as CredsspServerProcessGenerator;
-use secrecy::ExposeSecret as _;
 use ironrdp_connector::credssp::CredsspProcessGenerator as CredsspClientProcessGenerator;
 use ironrdp_connector::sspi;
 use ironrdp_connector::sspi::generator::{GeneratorState, NetworkRequest};
 use ironrdp_pdu::{mcs, nego, x224};
+use secrecy::ExposeSecret as _;
 use tokio::io::{AsyncRead, AsyncWrite, AsyncWriteExt};
 use typed_builder::TypedBuilder;
 
@@ -131,8 +131,12 @@ where
                 salt: _,
             } = user;
 
-            // The username is an the FQDN format. Thus, the domain field can be empty.
-            sspi::CredentialsBuffers::AuthIdentity(sspi::AuthIdentityBuffers::from_utf8(fqdn, "", password.expose_secret()))
+            // The username is in the FQDN format. Thus, the domain field can be empty.
+            sspi::CredentialsBuffers::AuthIdentity(sspi::AuthIdentityBuffers::from_utf8(
+                fqdn,
+                "",
+                password.expose_secret(),
+            ))
         });
 
         Some(sspi::KerberosServerConfig {