diff --git a/rust/Cargo.lock b/rust/Cargo.lock
index 0369dc8d94b6..f6342e002186 100644
--- a/rust/Cargo.lock
+++ b/rust/Cargo.lock
@@ -5883,6 +5883,7 @@ dependencies = [
  "itertools 0.14.0",
  "libc",
  "llm-multimodal",
+ "openssl",
  "prost",
  "prost-types",
  "rmp-serde",
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 455e660bcfee..3f6fac02562b 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -55,6 +55,8 @@ native-tls-vendored = { package = "native-tls", version = "0.2.18", features = [
 ndarray = { version = "0.16.1", features = ["serde"] }
 openai-harmony = "0.0.8"
 openai-protocol = "1.6.0"
+# For linking the system OpenSSL (ie. on systems with FIPS enabled)
+openssl = "0.10"
 parking_lot = "0.12.5"
 paste = "1.0.15"
 prometheus-client = "0.24.0"
@@ -65,7 +67,8 @@ pyo3 = "0.28.3"
 pythonize = "0.28.0"
 rand = "0.9.2"
 reasoning-parser = "1.2.2"
-reqwest = { version = "0.12.8", default-features = false, features = ["rustls-tls"] }
+# NOTE: TLS backend selected per-build by vllm-chat features (rustls / openssl)
+reqwest = { version = "0.12.8", default-features = false }
 riptoken = { version = "0.3.0", default-features = false }
 rmp-serde = "1.3.1"
 rmpv = { version = "1.3.1", features = ["with-serde"] }
@@ -112,13 +115,14 @@ tracing-subscriber = { version = "0.3.20", features = ["env-filter", "fmt"] }
 trait-set = "0.3.0"
 uuid = { version = "1.22.0", features = ["v4"] }
 validator = { version = "0.20.0", features = ["derive"] }
-vllm-chat = { path = "src/chat" }
+# NOTE: default-features = false so the backend is chosen explicitly
+vllm-chat = { path = "src/chat", default-features = false }
 vllm-engine-core-client = { path = "src/engine-core-client" }
 vllm-llm = { path = "src/llm" }
 vllm-managed-engine = { path = "src/managed-engine" }
 vllm-metrics = { path = "src/metrics" }
 vllm-reasoning-parser = { path = "src/reasoning-parser" }
-vllm-server = { path = "src/server" }
+vllm-server = { path = "src/server", default-features = false }
 vllm-text = { path = "src/text" }
 vllm-tokenizer = { path = "src/tokenizer" }
 vllm-tool-parser = { path = "src/tool-parser" }
diff --git a/rust/src/chat/Cargo.toml b/rust/src/chat/Cargo.toml
index 0523b9defe93..f5a133ae8df0 100644
--- a/rust/src/chat/Cargo.toml
+++ b/rust/src/chat/Cargo.toml
@@ -4,6 +4,11 @@ version.workspace = true
 edition.workspace = true
 license.workspace = true
 
+[features]
+default = ["rustls"]
+rustls = ["reqwest/rustls-tls"]
+openssl = ["reqwest/native-tls"]
+
 [dependencies]
 anyhow.workspace = true
 asynk-strim-attr.workspace = true
diff --git a/rust/src/cmd/Cargo.toml b/rust/src/cmd/Cargo.toml
index b0caa65b4e8c..17d5a8b8f275 100644
--- a/rust/src/cmd/Cargo.toml
+++ b/rust/src/cmd/Cargo.toml
@@ -9,7 +9,9 @@ name = "vllm-rs"
 path = "src/main.rs"
 
 [features]
-default = []
+default = ["rustls"]
+rustls = ["vllm-server/rustls"]
+openssl = ["vllm-server/openssl"]
 native-tls-vendored = ["dep:native-tls-vendored"]
 
 [dependencies]
diff --git a/rust/src/server/Cargo.toml b/rust/src/server/Cargo.toml
index cb62f3376bc6..d5a2b775d4dc 100644
--- a/rust/src/server/Cargo.toml
+++ b/rust/src/server/Cargo.toml
@@ -4,6 +4,13 @@ version.workspace = true
 edition.workspace = true
 license.workspace = true
 
+[features]
+default = ["rustls"]
+# Features are additive so Cargo's `--all-features` mode remains valid; use
+# `--no-default-features --features openssl` for OpenSSL-only builds.
+rustls = ["dep:sha2", "dep:subtle", "vllm-chat/rustls"]
+openssl = ["dep:openssl", "vllm-chat/openssl"]
+
 [dependencies]
 anyhow.workspace = true
 asynk-strim-attr.workspace = true
@@ -14,15 +21,16 @@ http-body.workspace = true
 itertools.workspace = true
 libc.workspace = true
 llm-multimodal.workspace = true
+openssl = { workspace = true, optional = true }
 prost.workspace = true
 prost-types.workspace = true
 rmpv.workspace = true
 serde.workspace = true
 serde_json.workspace = true
 serde_with.workspace = true
-sha2.workspace = true
+sha2 = { workspace = true, optional = true }
 socket2.workspace = true
-subtle.workspace = true
+subtle = { workspace = true, optional = true }
 thiserror-ext.workspace = true
 tokio.workspace = true
 tokio-stream.workspace = true
diff --git a/rust/src/server/src/middleware/auth.rs b/rust/src/server/src/middleware/auth.rs
index 696e30615a87..afacd973b695 100644
--- a/rust/src/server/src/middleware/auth.rs
+++ b/rust/src/server/src/middleware/auth.rs
@@ -62,17 +62,34 @@ fn verify_token(authorization: Option<&HeaderValue>, api_key_hashes: &[ApiKeyHas
     token_match
 }
 
+#[cfg(not(feature = "openssl"))]
 fn constant_time_eq(left: &ApiKeyHash, right: &ApiKeyHash) -> bool {
     use subtle::ConstantTimeEq;
 
     bool::from(left.ct_eq(right))
 }
 
+#[cfg(feature = "openssl")]
+fn constant_time_eq(left: &ApiKeyHash, right: &ApiKeyHash) -> bool {
+    openssl::memcmp::eq(left, right)
+}
+
 #[cfg(test)]
 mod tests {
     use super::constant_time_eq;
     use crate::state::hash_api_key;
 
+    // SHA-256("abc"); pins both backends to the same NIST vector.
+    #[test]
+    fn hash_api_key_matches_nist_sha256_vector() {
+        const SHA256_ABC: [u8; 32] = [
+            0xba, 0x78, 0x16, 0xbf, 0x8f, 0x01, 0xcf, 0xea, 0x41, 0x41, 0x40, 0xde, 0x5d, 0xae,
+            0x22, 0x23, 0xb0, 0x03, 0x61, 0xa3, 0x96, 0x17, 0x7a, 0x9c, 0xb4, 0x10, 0xff, 0x61,
+            0xf2, 0x00, 0x15, 0xad,
+        ];
+        assert_eq!(hash_api_key("abc"), SHA256_ABC);
+    }
+
     #[test]
     fn constant_time_eq_checks_sha256_digests() {
         assert!(constant_time_eq(
diff --git a/rust/src/server/src/state.rs b/rust/src/server/src/state.rs
index 0be074dff88c..cdf7566586fc 100644
--- a/rust/src/server/src/state.rs
+++ b/rust/src/server/src/state.rs
@@ -2,7 +2,6 @@ use std::sync::Arc;
 use std::sync::atomic::{AtomicU64, Ordering};
 
 use serde_json::Value;
-use sha2::{Digest, Sha256};
 use tokio::time::{Duration, Instant, sleep_until};
 use tracing::warn;
 use vllm_chat::ChatLlm;
@@ -17,10 +16,18 @@ const SHUTDOWN_REFCOUNT_POLL_INTERVAL: Duration = Duration::from_millis(100);
 
 pub(crate) type ApiKeyHash = [u8; 32];
 
+#[cfg(not(feature = "openssl"))]
 pub(crate) fn hash_api_key(api_key: &str) -> ApiKeyHash {
+    use sha2::{Digest, Sha256};
+
     Sha256::digest(api_key.as_bytes()).into()
 }
 
+#[cfg(feature = "openssl")]
+pub(crate) fn hash_api_key(api_key: &str) -> ApiKeyHash {
+    openssl::sha::sha256(api_key.as_bytes())
+}
+
 /// Shared router state for the minimal single-model OpenAI server.
 pub struct AppState {
     /// All public model IDs served by this frontend. The first entry is the