diff --git a/Cargo.toml b/Cargo.toml
index 9806461b..37d81fe7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -200,6 +200,15 @@ path = "src/bin/opaque-hurl-helper.rs"
 # blinding, AKE nonces are per-attempt-random). Not shipped in the
 # release Dockerfile (nothing outside tests/ calls it).
 
+[[bin]]
+name = "dpop-hurl-helper"
+path = "src/bin/dpop-hurl-helper.rs"
+# Test-suite DPoP client — signs an ES256 proof per request, threads
+# the DPoP-Nonce challenge/retry loop, and covers the wire-protocol
+# scenarios Hurl can't express (per-request fresh jti/iat, replay
+# detection, malformed proofs, wrong htm/htu/alg/typ). Same
+# no-ship-in-release status as opaque-hurl-helper.
+
 [[bin]]
 name = "load-seed"
 path = "src/bin/load-seed.rs"
diff --git a/src/bin/dpop-hurl-helper.rs b/src/bin/dpop-hurl-helper.rs
new file mode 100644
index 00000000..3a0ed0d8
--- /dev/null
+++ b/src/bin/dpop-hurl-helper.rs
@@ -0,0 +1,689 @@
+//! DPoP wire-protocol test helper for the api-test suite.
+//!
+//! Hurl can't drive DPoP: every proof carries a fresh `jti`, a
+//! current `iat`, an `htm`/`htu` matching the exact request, an
+//! ES256 signature from a persistent browser-held keypair, and a
+//! nonce threaded from the server's `DPoP-Nonce` response header.
+//! A declarative `.hurl` template has no way to compute that per
+//! request. Same problem OPAQUE has, same solution:
+//! `opaque-hurl-helper.rs` (task #19) verifies OPAQUE end-to-end;
+//! this binary does the same for DPoP.
+//!
+//! Invocation (from `tests/api/run.sh`):
+//!
+//! ```bash
+//! OXICLOUD_DPOP_MODE=required
+//! DPOP_HELPER_BASE_URL=$base_url \
+//! DPOP_HELPER_USERNAME=$username \
+//! DPOP_HELPER_PASSWORD=$password \
+//!     ./target/debug/dpop-hurl-helper
+//! ```
+//!
+//! Exit codes:
+//!   * 0 — every scenario succeeded.
+//!   * 1 — any scenario failed; diagnostic on stderr.
+//!
+//! Scope: this binary covers the wire contract for the currently-
+//! integrated slice — verifier + nonce + replay + middleware in
+//! opportunistic mode. Scenarios requiring session-context binding
+//! (bound-vs-unbound enforcement per `session.dpop_jkt`, refresh
+//! continuity, thumbprint mismatch vs stored) are deferred until
+//! Gate 7 threads session context through the middleware.
+
+use base64::Engine as _;
+use base64::engine::general_purpose::{STANDARD as B64, URL_SAFE_NO_PAD as B64_URL_NO_PAD};
+use opaque_ke::{ClientLogin, ClientLoginFinishParameters, CredentialResponse};
+use p256::ecdsa::signature::Signer;
+use p256::ecdsa::{Signature, SigningKey};
+use rand_core::OsRng as OpaqueRng;
+use serde_json::json;
+use sha2::{Digest, Sha256};
+use std::process::ExitCode;
+
+// Reuse the concrete ciphersuite the production `OpaqueService` uses —
+// mismatching client + server suites would fail every handshake with
+// a confusing error.
+use oxicloud::infrastructure::services::opaque_service::OxiCloudSuite;
+
+/// Server may emit URL_SAFE_NO_PAD *or* STANDARD base64; try both so
+/// a future format flip doesn't silently break the round-trip.
+fn decode_opaque_b64(input: &str) -> Result<Vec<u8>, base64::DecodeError> {
+    let s = input.trim();
+    B64_URL_NO_PAD.decode(s).or_else(|_| B64.decode(s))
+}
+
+#[derive(serde::Deserialize)]
+struct OpaqueParamsResp {
+    enabled: bool,
+    #[serde(rename = "ciphersuiteVersion")]
+    _ciphersuite_version: i16,
+    ksf: OpaqueKsfParams,
+}
+
+#[derive(serde::Deserialize)]
+struct OpaqueKsfParams {
+    #[serde(rename = "memoryKib")]
+    memory_kib: u32,
+    iterations: u32,
+    parallelism: u32,
+}
+
+#[derive(serde::Deserialize)]
+struct OpaqueKe1Resp {
+    #[serde(rename = "exchangeId")]
+    exchange_id: String,
+    #[serde(rename = "loginResponse")]
+    login_response: String,
+}
+
+const EXIT_FAIL: u8 = 1;
+
+fn env_or_fail(key: &str) -> String {
+    std::env::var(key).unwrap_or_else(|_| {
+        eprintln!("dpop-hurl-helper: required env var {key} unset");
+        std::process::exit(EXIT_FAIL as i32);
+    })
+}
+
+fn fail(msg: impl std::fmt::Display) -> ExitCode {
+    // Bordered banner so a failure stands out against the interleaved
+    // server audit log — the last line before this is usually the
+    // server-side reject that caused it, which visually blends in.
+    eprintln!();
+    eprintln!("┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓");
+    eprintln!("┃ dpop-hurl-helper: FAIL                                                      ┃");
+    eprintln!("┃   {msg}");
+    eprintln!("┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛");
+    ExitCode::from(EXIT_FAIL)
+}
+
+fn now_secs() -> i64 {
+    std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|d| d.as_secs() as i64)
+        .unwrap_or(0)
+}
+
+fn random_jti() -> String {
+    // 16 bytes of OS randomness, base64url'd — plenty of entropy for
+    // per-request uniqueness; the server's replay cache keys on this.
+    use p256::elliptic_curve::rand_core::{OsRng, RngCore};
+    let mut b = [0u8; 16];
+    OsRng.fill_bytes(&mut b);
+    B64_URL_NO_PAD.encode(b)
+}
+
+/// A persistent-across-scenarios keypair — simulates one browser
+/// tab whose IndexedDB entry survives every scenario in this run.
+struct KeyBundle {
+    signing_key: SigningKey,
+    jwk_x_b64: String,
+    jwk_y_b64: String,
+}
+
+impl KeyBundle {
+    fn fresh() -> Self {
+        // Deterministic-ish seed — this is a test tool, not a
+        // security surface. Skipping `rand`-dep to keep the binary
+        // dep footprint identical to what Gate 5 already added.
+        let mut bytes = [0u8; 32];
+        for (i, b) in bytes.iter_mut().enumerate() {
+            *b = ((i as u8).wrapping_mul(37)).wrapping_add(1);
+        }
+        let signing_key = SigningKey::from_bytes(&bytes.into()).expect("valid P-256 scalar");
+        let vkey = signing_key.verifying_key();
+        let enc = vkey.to_encoded_point(false);
+        Self {
+            signing_key,
+            jwk_x_b64: B64_URL_NO_PAD.encode(enc.x().unwrap()),
+            jwk_y_b64: B64_URL_NO_PAD.encode(enc.y().unwrap()),
+        }
+    }
+}
+
+/// Overrides for building malformed / tampered proofs, per scenario.
+#[derive(Default, Clone)]
+struct ProofOverrides<'a> {
+    override_alg: Option<&'a str>,
+    override_typ: Option<&'a str>,
+    override_htm: Option<&'a str>,
+    override_htu: Option<&'a str>,
+    stale_iat: bool,
+    /// If `Some`, use this exact string for the `jti` instead of a
+    /// fresh random one — the replay scenario needs to reuse it.
+    fixed_jti: Option<String>,
+    /// If `Some`, include this literal `nonce` claim (even if it's
+    /// wrong on purpose). If `None`, use whatever the caller
+    /// tracked from `DPoP-Nonce` response headers.
+    force_nonce: Option<String>,
+}
+
+/// Build + sign a DPoP proof against the given method + URL.
+/// `nonce` is the current server-issued nonce (if any); `overrides`
+/// let scenario code tamper with the proof shape.
+fn build_proof(
+    keys: &KeyBundle,
+    method: &str,
+    url: &str,
+    nonce: Option<&str>,
+    overrides: &ProofOverrides<'_>,
+) -> String {
+    let header = json!({
+        "typ": overrides.override_typ.unwrap_or("dpop+jwt"),
+        "alg": overrides.override_alg.unwrap_or("ES256"),
+        "jwk": {
+            "crv": "P-256",
+            "kty": "EC",
+            "x": keys.jwk_x_b64,
+            "y": keys.jwk_y_b64,
+        },
+    });
+    let iat = if overrides.stale_iat {
+        now_secs() - 10_000
+    } else {
+        now_secs()
+    };
+    let mut claims = json!({
+        "htm": overrides.override_htm.unwrap_or(method),
+        "htu": overrides.override_htu.map(str::to_owned).unwrap_or_else(|| canonical_htu(url)),
+        "iat": iat,
+        "jti": overrides.fixed_jti.clone().unwrap_or_else(random_jti),
+    });
+    let nonce_to_use = overrides.force_nonce.as_deref().or(nonce);
+    if let Some(n) = nonce_to_use {
+        claims.as_object_mut().unwrap().insert(
+            "nonce".to_string(),
+            serde_json::Value::String(n.to_string()),
+        );
+    }
+
+    let h_b64 = B64_URL_NO_PAD.encode(header.to_string());
+    let p_b64 = B64_URL_NO_PAD.encode(claims.to_string());
+    let signing_input = format!("{h_b64}.{p_b64}");
+    let sig: Signature = keys.signing_key.sign(signing_input.as_bytes());
+    let s_b64 = B64_URL_NO_PAD.encode(sig.to_bytes());
+    format!("{h_b64}.{p_b64}.{s_b64}")
+}
+
+fn canonical_htu(url: &str) -> String {
+    let u = reqwest::Url::parse(url).expect("valid URL for htu");
+    format!("{}://{}{}", u.scheme(), u.authority(), u.path())
+}
+
+/// Log in via OPAQUE, return the access + refresh tokens.
+///
+/// `opaque-hurl-helper` runs earlier in `tests/api/run.sh` and
+/// mints the OPAQUE envelope for `admin`; from that point on the
+/// account is migrated and legacy `POST /api/auth/login` refuses
+/// with Phase-4 `opaque_migrated_use_opaque` (403). So this
+/// helper drives the OPAQUE handshake directly — same ciphersuite
+/// (`OxiCloudSuite`) and same `/params` KSF-fetch pattern as
+/// `opaque-hurl-helper`. Long-term this is also what OPAQUE-only
+/// mode (`docs/plan/opaque-only.md`) requires: legacy login is
+/// on the way out entirely.
+async fn opaque_login(
+    http: &reqwest::Client,
+    base: &str,
+    username: &str,
+    password: &str,
+) -> Result<(String, String), String> {
+    // Fetch server params so client-side Argon2 matches. Per Phase B
+    // the envelope's OWN KSF is authoritative for that user (via
+    // `/login/lookup`), but for a test admin whose envelope was
+    // freshly minted by the OPAQUE helper the two match, so
+    // `/params` is sufficient here.
+    let params: OpaqueParamsResp = http
+        .get(format!("{base}/api/auth/opaque/params"))
+        .send()
+        .await
+        .map_err(|e| format!("opaque /params: {e}"))?
+        .json()
+        .await
+        .map_err(|e| format!("parse /params: {e}"))?;
+    if !params.enabled {
+        return Err("server reports OPAQUE disabled — did opaque-hurl-helper run first?".into());
+    }
+    let ksf_params = argon2::Params::new(
+        params.ksf.memory_kib,
+        params.ksf.iterations,
+        params.ksf.parallelism,
+        None,
+    )
+    .map_err(|e| format!("build Argon2 params: {e}"))?;
+    let ksf = argon2::Argon2::new(
+        argon2::Algorithm::Argon2id,
+        argon2::Version::V0x13,
+        ksf_params,
+    );
+
+    let mut rng = OpaqueRng;
+
+    // ── KE1 — public endpoint, no bearer ─────────────────────────────
+    let client_login = ClientLogin::<OxiCloudSuite>::start(&mut rng, password.as_bytes())
+        .map_err(|e| format!("ClientLogin::start: {e}"))?;
+    let ke1_body = json!({
+        "userIdentifier": username,
+        "startLoginRequest": B64.encode(client_login.message.serialize()),
+    });
+    let ke1_res = http
+        .post(format!("{base}/api/auth/opaque/login/ke1"))
+        .json(&ke1_body)
+        .send()
+        .await
+        .map_err(|e| format!("ke1 POST: {e}"))?;
+    if !ke1_res.status().is_success() {
+        return Err(format!("ke1 returned {}", ke1_res.status()));
+    }
+    let ke1: OpaqueKe1Resp = ke1_res
+        .json()
+        .await
+        .map_err(|e| format!("parse ke1: {e}"))?;
+    let cred_bytes =
+        decode_opaque_b64(&ke1.login_response).map_err(|e| format!("decode loginResponse: {e}"))?;
+    let cred_response = CredentialResponse::<OxiCloudSuite>::deserialize(&cred_bytes)
+        .map_err(|e| format!("deserialize CredentialResponse: {e}"))?;
+
+    // ── KE3 — finish + submit ─────────────────────────────────────────
+    let login_finish = client_login
+        .state
+        .finish(
+            password.as_bytes(),
+            cred_response,
+            ClientLoginFinishParameters::new(None, opaque_ke::Identifiers::default(), Some(&ksf)),
+        )
+        .map_err(|e| format!("ClientLogin::finish (bad password?): {e}"))?;
+    // URL_SAFE_NO_PAD on the wire — matches what the SPA sends and
+    // what the server's handler prefers (accepts both, but this is
+    // the canonical form).
+    let ke3_body = json!({
+        "exchangeId": ke1.exchange_id,
+        "finishLoginRequest": B64_URL_NO_PAD.encode(login_finish.message.serialize()),
+    });
+    let ke3_res = http
+        .post(format!("{base}/api/auth/opaque/login/ke3"))
+        .json(&ke3_body)
+        .send()
+        .await
+        .map_err(|e| format!("ke3 POST: {e}"))?;
+    if !ke3_res.status().is_success() {
+        return Err(format!("ke3 returned {}", ke3_res.status()));
+    }
+    let body: serde_json::Value = ke3_res.json().await.map_err(|e| format!("ke3 body: {e}"))?;
+    let access = body["access_token"]
+        .as_str()
+        .ok_or("ke3 response missing access_token")?
+        .to_string();
+    let refresh = body["refresh_token"]
+        .as_str()
+        .ok_or("ke3 response missing refresh_token")?
+        .to_string();
+    Ok((access, refresh))
+}
+
+/// Send a GET request to `path` with a DPoP proof, following the
+/// nonce-challenge retry loop. Returns the final response + the
+/// nonce currently cached (which the caller threads into follow-up
+/// requests).
+async fn get_with_dpop(
+    http: &reqwest::Client,
+    base: &str,
+    path: &str,
+    access_token: &str,
+    keys: &KeyBundle,
+    cached_nonce: Option<String>,
+    overrides: &ProofOverrides<'_>,
+) -> Result<(reqwest::Response, Option<String>), String> {
+    let url = format!("{base}{path}");
+    let proof = build_proof(keys, "GET", &url, cached_nonce.as_deref(), overrides);
+    let res = http
+        .get(&url)
+        .bearer_auth(access_token)
+        .header("DPoP", proof)
+        .send()
+        .await
+        .map_err(|e| format!("GET {path}: {e}"))?;
+    // Harvest DPoP-Nonce even on failure — the server stamps it
+    // regardless so the client can retry with the fresh value.
+    let updated_nonce = res
+        .headers()
+        .get("DPoP-Nonce")
+        .and_then(|v| v.to_str().ok())
+        .map(str::to_owned)
+        .or(cached_nonce);
+    // Challenge-retry once — mirrors the SPA fetch interceptor.
+    if res.status() == 401
+        && res
+            .headers()
+            .get("WWW-Authenticate")
+            .and_then(|v| v.to_str().ok())
+            .is_some_and(|v| v.contains("use_dpop_nonce"))
+    {
+        // Only ONE retry — a second challenge on the retry is a
+        // server bug and should surface as-is.
+        let proof2 = build_proof(keys, "GET", &url, updated_nonce.as_deref(), overrides);
+        let res2 = http
+            .get(&url)
+            .bearer_auth(access_token)
+            .header("DPoP", proof2)
+            .send()
+            .await
+            .map_err(|e| format!("GET {path} (retry): {e}"))?;
+        let updated_nonce2 = res2
+            .headers()
+            .get("DPoP-Nonce")
+            .and_then(|v| v.to_str().ok())
+            .map(str::to_owned)
+            .or(updated_nonce);
+        return Ok((res2, updated_nonce2));
+    }
+    Ok((res, updated_nonce))
+}
+
+fn expect_status(scenario: &str, res: &reqwest::Response, want: u16) -> Result<(), String> {
+    if res.status().as_u16() == want {
+        Ok(())
+    } else {
+        Err(format!(
+            "scenario {scenario}: expected HTTP {want}, got {}",
+            res.status()
+        ))
+    }
+}
+
+// Defensive-programming pattern: every scenario refreshes the
+// cached nonce so a later scenario picks up any rotation the
+// server did in between. Scenarios that DON'T re-consume the
+// cached nonce (e.g. #6 which passes a bogus value on purpose)
+// look like dead assignments to the linter — silence it here
+// rather than sprinkle `let _ = n` calls that obscure intent.
+#[allow(unused_assignments)]
+#[tokio::main(flavor = "current_thread")]
+async fn main() -> ExitCode {
+    let base = env_or_fail("DPOP_HELPER_BASE_URL");
+    let username = env_or_fail("DPOP_HELPER_USERNAME");
+    let password = env_or_fail("DPOP_HELPER_PASSWORD");
+    let base = base.trim_end_matches('/');
+
+    let http = match reqwest::Client::builder()
+        .timeout(std::time::Duration::from_secs(15))
+        .build()
+    {
+        Ok(c) => c,
+        Err(e) => return fail(format!("build reqwest client: {e}")),
+    };
+
+    // ── 1. Log in via OPAQUE (session created unbound — Gate 3
+    //       requires the client to send `dpop_jkt` in the login
+    //       body; this helper doesn't, so we get the fail-open
+    //       unbound path). Bind support gets tested via
+    //       `POST /api/auth/dpop/bind` in a later gate.
+    //
+    //       OPAQUE (not legacy) because `opaque-hurl-helper`
+    //       migrates `admin` earlier in `run.sh`, after which
+    //       legacy login 403s with Phase-4 refusal — and once
+    //       OPAQUE-only mode ships (`docs/plan/opaque-only.md`)
+    //       there IS no legacy path anyway.
+    let (access, _refresh) = match opaque_login(&http, base, &username, &password).await {
+        Ok(t) => t,
+        Err(e) => return fail(e),
+    };
+
+    let keys = KeyBundle::fresh();
+    let jkt = {
+        // Compute expected thumbprint for logging — server ignores
+        // at this gate but future scenarios will compare.
+        let canonical = format!(
+            r#"{{"crv":"P-256","kty":"EC","x":"{}","y":"{}"}}"#,
+            keys.jwk_x_b64, keys.jwk_y_b64
+        );
+        B64_URL_NO_PAD.encode(Sha256::digest(canonical.as_bytes()))
+    };
+    eprintln!("dpop-hurl-helper: keypair jkt={jkt}");
+
+    let mut nonce: Option<String> = None;
+
+    // ── Scenario 1: happy path — bootstrap (no nonce) → challenge
+    //    → retry with nonce → 200. The retry loop is inside
+    //    `get_with_dpop`.
+    let (res, n) = match get_with_dpop(
+        &http,
+        base,
+        "/api/auth/me",
+        &access,
+        &keys,
+        nonce.clone(),
+        &ProofOverrides::default(),
+    )
+    .await
+    {
+        Ok(t) => t,
+        Err(e) => return fail(e),
+    };
+    if let Err(e) = expect_status("happy_path", &res, 200) {
+        return fail(e);
+    }
+    if n.is_none() {
+        return fail("happy_path: server did not stamp DPoP-Nonce on response");
+    }
+    nonce = n;
+    eprintln!(
+        "dpop-hurl-helper: scenario 1 (happy path) ✓  cached_nonce={:?}",
+        nonce
+    );
+
+    // ── Scenario 2: wrong htm — sign for POST but send GET → 401
+    let (res, n) = match get_with_dpop(
+        &http,
+        base,
+        "/api/auth/me",
+        &access,
+        &keys,
+        nonce.clone(),
+        &ProofOverrides {
+            override_htm: Some("POST"),
+            ..Default::default()
+        },
+    )
+    .await
+    {
+        Ok(t) => t,
+        Err(e) => return fail(e),
+    };
+    nonce = n;
+    if let Err(e) = expect_status("wrong_htm", &res, 401) {
+        return fail(e);
+    }
+    eprintln!("dpop-hurl-helper: scenario 2 (wrong htm) ✓");
+
+    // ── Scenario 3: wrong htu — sign for /api/foo but send /api/auth/me → 401
+    let (res, n) = match get_with_dpop(
+        &http,
+        base,
+        "/api/auth/me",
+        &access,
+        &keys,
+        nonce.clone(),
+        &ProofOverrides {
+            override_htu: Some("https://not-this-host.example/api/foo"),
+            ..Default::default()
+        },
+    )
+    .await
+    {
+        Ok(t) => t,
+        Err(e) => return fail(e),
+    };
+    nonce = n;
+    if let Err(e) = expect_status("wrong_htu", &res, 401) {
+        return fail(e);
+    }
+    eprintln!("dpop-hurl-helper: scenario 3 (wrong htu) ✓");
+
+    // ── Scenario 4: wrong alg (RS256) — 401
+    let (res, n) = match get_with_dpop(
+        &http,
+        base,
+        "/api/auth/me",
+        &access,
+        &keys,
+        nonce.clone(),
+        &ProofOverrides {
+            override_alg: Some("RS256"),
+            ..Default::default()
+        },
+    )
+    .await
+    {
+        Ok(t) => t,
+        Err(e) => return fail(e),
+    };
+    nonce = n;
+    if let Err(e) = expect_status("wrong_alg", &res, 401) {
+        return fail(e);
+    }
+    eprintln!("dpop-hurl-helper: scenario 4 (wrong alg) ✓");
+
+    // ── Scenario 5: wrong typ — 401
+    let (res, n) = match get_with_dpop(
+        &http,
+        base,
+        "/api/auth/me",
+        &access,
+        &keys,
+        nonce.clone(),
+        &ProofOverrides {
+            override_typ: Some("jwt"),
+            ..Default::default()
+        },
+    )
+    .await
+    {
+        Ok(t) => t,
+        Err(e) => return fail(e),
+    };
+    nonce = n;
+    if let Err(e) = expect_status("wrong_typ", &res, 401) {
+        return fail(e);
+    }
+    eprintln!("dpop-hurl-helper: scenario 5 (wrong typ) ✓");
+
+    // ── Scenario 6: stale nonce — simulate the client's cached
+    //    nonce having expired server-side (server restarted, or
+    //    pool TTL elapsed). The server issues a challenge with a
+    //    fresh nonce, and `get_with_dpop` MUST retry once using
+    //    that fresh value from the response header — not the
+    //    stale one from `cached_nonce`.
+    //
+    //    Pass the bogus value positionally (via `cached_nonce`)
+    //    rather than through the `force_nonce` override — the
+    //    override would survive the retry and cause a second
+    //    challenge, defeating the recovery path we're testing.
+    let (res, n) = match get_with_dpop(
+        &http,
+        base,
+        "/api/auth/me",
+        &access,
+        &keys,
+        Some("nonce-that-server-does-not-know".to_string()),
+        &ProofOverrides::default(),
+    )
+    .await
+    {
+        Ok(t) => t,
+        Err(e) => return fail(e),
+    };
+    if let Err(e) = expect_status("stale_nonce_challenge_retry", &res, 200) {
+        return fail(e);
+    }
+    nonce = n;
+    eprintln!("dpop-hurl-helper: scenario 6 (stale nonce → challenge → retry) ✓");
+
+    // ── Scenario 7: replay — build a proof, send it TWICE with
+    //    the same jti; second call must be replay-rejected.
+    //    Uses a bespoke send (no retry-loop) so we control both
+    //    submissions of the exact-same bytes.
+    let fixed_jti = random_jti();
+    let url = format!("{base}/api/auth/me");
+    let proof_replay = build_proof(
+        &keys,
+        "GET",
+        &url,
+        nonce.as_deref(),
+        &ProofOverrides {
+            fixed_jti: Some(fixed_jti.clone()),
+            ..Default::default()
+        },
+    );
+    let res_first = match http
+        .get(&url)
+        .bearer_auth(&access)
+        .header("DPoP", proof_replay.clone())
+        .send()
+        .await
+    {
+        Ok(r) => r,
+        Err(e) => return fail(format!("replay send 1: {e}")),
+    };
+    if let Err(e) = expect_status("replay_first_send", &res_first, 200) {
+        return fail(e);
+    }
+    let res_second = match http
+        .get(&url)
+        .bearer_auth(&access)
+        .header("DPoP", proof_replay)
+        .send()
+        .await
+    {
+        Ok(r) => r,
+        Err(e) => return fail(format!("replay send 2: {e}")),
+    };
+    if let Err(e) = expect_status("replay_second_send", &res_second, 401) {
+        return fail(e);
+    }
+    // The replay 401 is an invalid_dpop_proof shape (not use_dpop_nonce)
+    let www_auth = res_second
+        .headers()
+        .get("WWW-Authenticate")
+        .and_then(|v| v.to_str().ok())
+        .unwrap_or("");
+    if www_auth.contains("use_dpop_nonce") {
+        return fail(format!(
+            "replay: WWW-Authenticate should be invalid_dpop_proof, was: {www_auth}"
+        ));
+    }
+    eprintln!("dpop-hurl-helper: scenario 7 (replay) ✓");
+
+    // ── Scenario 8: malformed JWS — send garbage in the DPoP
+    //    header. Server-side verifier rejects at the split step.
+    let res = match http
+        .get(&url)
+        .bearer_auth(&access)
+        .header("DPoP", "not-a-real-jws")
+        .send()
+        .await
+    {
+        Ok(r) => r,
+        Err(e) => return fail(format!("malformed send: {e}")),
+    };
+    if let Err(e) = expect_status("malformed", &res, 401) {
+        return fail(e);
+    }
+    eprintln!("dpop-hurl-helper: scenario 8 (malformed) ✓");
+
+    // ── Scenario 9: no proof at all on a bound-if-required path.
+    //    In opportunistic mode this passes through; in required
+    //    mode the session is unbound (`dpop_jkt IS NULL`) so it
+    //    STILL passes through. Server-side gate 9 will flip this
+    //    once session-context enforcement lands.
+    let res_no_proof = match http.get(&url).bearer_auth(&access).send().await {
+        Ok(r) => r,
+        Err(e) => return fail(format!("no_proof send: {e}")),
+    };
+    if let Err(e) = expect_status("no_proof_unbound_session", &res_no_proof, 200) {
+        return fail(e);
+    }
+    eprintln!("dpop-hurl-helper: scenario 9 (no proof, unbound session → pass) ✓");
+
+    eprintln!("dpop-hurl-helper: all scenarios passed");
+    ExitCode::SUCCESS
+}
diff --git a/src/main.rs b/src/main.rs
index 29661296..6fd1af72 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -780,6 +780,10 @@ async fn run() -> Result<(), Box<dyn std::error::Error>> {
                 app_state.clone(),
                 require_no_password_change_pending_layer,
             ))
+            .layer(axum::middleware::from_fn_with_state(
+                app_state.clone(),
+                require_dpop_layer,
+            ))
             .layer(axum::middleware::from_fn(csrf_middleware))
             .layer(axum::middleware::from_fn_with_state(
                 app_state.clone(),
@@ -792,6 +796,10 @@ async fn run() -> Result<(), Box<dyn std::error::Error>> {
                 app_state.clone(),
                 require_no_password_change_pending_layer,
             ))
+            .layer(axum::middleware::from_fn_with_state(
+                app_state.clone(),
+                require_dpop_layer,
+            ))
             .layer(axum::middleware::from_fn(csrf_middleware))
             .layer(axum::middleware::from_fn_with_state(
                 app_state.clone(),
@@ -814,6 +822,10 @@ async fn run() -> Result<(), Box<dyn std::error::Error>> {
                     app_state.clone(),
                     require_no_password_change_pending_layer,
                 ))
+                .layer(axum::middleware::from_fn_with_state(
+                    app_state.clone(),
+                    require_dpop_layer,
+                ))
                 .layer(axum::middleware::from_fn(csrf_middleware))
                 .layer(axum::middleware::from_fn_with_state(
                     app_state.clone(),
@@ -851,6 +863,10 @@ async fn run() -> Result<(), Box<dyn std::error::Error>> {
                 app_state.clone(),
                 require_no_password_change_pending_layer,
             ))
+            .layer(axum::middleware::from_fn_with_state(
+                app_state.clone(),
+                require_dpop_layer,
+            ))
             .layer(axum::middleware::from_fn(csrf_middleware))
             .layer(axum::middleware::from_fn_with_state(
                 app_state.clone(),
@@ -864,6 +880,10 @@ async fn run() -> Result<(), Box<dyn std::error::Error>> {
                 app_state.clone(),
                 require_no_password_change_pending_layer,
             ))
+            .layer(axum::middleware::from_fn_with_state(
+                app_state.clone(),
+                require_dpop_layer,
+            ))
             .layer(axum::middleware::from_fn(csrf_middleware))
             .layer(axum::middleware::from_fn_with_state(
                 app_state.clone(),
@@ -885,6 +905,7 @@ async fn run() -> Result<(), Box<dyn std::error::Error>> {
         // change-password, and logout internally so the SPA can
         // complete the reset flow — see the middleware doc for the
         // allowlist and its rationale.
+        use oxicloud::interfaces::middleware::dpop::require_dpop_layer;
         use oxicloud::interfaces::middleware::user::{
             require_internal_user_layer, require_no_password_change_pending_layer,
         };
@@ -893,6 +914,10 @@ async fn run() -> Result<(), Box<dyn std::error::Error>> {
                 app_state.clone(),
                 require_no_password_change_pending_layer,
             ))
+            .layer(axum::middleware::from_fn_with_state(
+                app_state.clone(),
+                require_dpop_layer,
+            ))
             .layer(axum::middleware::from_fn_with_state(
                 app_state.clone(),
                 require_internal_user_layer,
@@ -906,6 +931,10 @@ async fn run() -> Result<(), Box<dyn std::error::Error>> {
                 app_state.clone(),
                 require_no_password_change_pending_layer,
             ))
+            .layer(axum::middleware::from_fn_with_state(
+                app_state.clone(),
+                require_dpop_layer,
+            ))
             .layer(axum::middleware::from_fn_with_state(
                 app_state.clone(),
                 require_internal_user_layer,
@@ -919,6 +948,10 @@ async fn run() -> Result<(), Box<dyn std::error::Error>> {
                 app_state.clone(),
                 require_no_password_change_pending_layer,
             ))
+            .layer(axum::middleware::from_fn_with_state(
+                app_state.clone(),
+                require_dpop_layer,
+            ))
             .layer(axum::middleware::from_fn_with_state(
                 app_state.clone(),
                 require_internal_user_layer,
diff --git a/tests/api/run.sh b/tests/api/run.sh
index b7213127..9c140eb1 100755
--- a/tests/api/run.sh
+++ b/tests/api/run.sh
@@ -248,4 +248,28 @@ OPAQUE_HELPER_USERNAME="$username" \
 OPAQUE_HELPER_PASSWORD="$password" \
   "$OPAQUE_HELPER_BIN" || die "OPAQUE crypto handshake failed"
 
+# ── 6. DPoP wire protocol — the parts Hurl can't drive ──────────────────
+# Each proof carries a fresh jti, current iat, htm/htu matching the
+# exact request, an ES256 signature, and a threaded nonce — none of
+# which a declarative .hurl template can compute. See
+# `src/bin/dpop-hurl-helper.rs` for the scenario matrix (happy path,
+# wrong htm/htu/alg/typ, stale nonce, replay, malformed, fail-open
+# when the session is unbound). Runs against the SAME server target
+# the OPAQUE helper used — but the server config must set
+# `OXICLOUD_DPOP_MODE=opportunistic` (or `required`) or the middleware
+# is a pass-through and every failure scenario silently 200s.
+DPOP_HELPER_BIN="$REPO_ROOT/target/$BUILD_TARGET/dpop-hurl-helper"
+if [[ ! -x "$DPOP_HELPER_BIN" ]]; then
+  log "Building dpop-hurl-helper ($BUILD_TARGET)..."
+  case "$BUILD_TARGET" in
+    debug)   (cd "$REPO_ROOT" && cargo build           --bin dpop-hurl-helper 2>&1 | tail -n 20) || die "dpop-hurl-helper build failed" ;;
+    release) (cd "$REPO_ROOT" && cargo build --release --bin dpop-hurl-helper 2>&1 | tail -n 20) || die "dpop-hurl-helper build failed" ;;
+  esac
+fi
+log "Running DPoP wire-protocol helper..."
+DPOP_HELPER_BASE_URL="$base_url" \
+DPOP_HELPER_USERNAME="$username" \
+DPOP_HELPER_PASSWORD="$password" \
+  "$DPOP_HELPER_BIN" || die "DPoP wire-protocol test failed"
+
 log "All tests passed."
diff --git a/tests/common/server.env b/tests/common/server.env
index 3fa08af1..2a0c4118 100644
--- a/tests/common/server.env
+++ b/tests/common/server.env
@@ -145,3 +145,14 @@ OXICLOUD_AUTH_OPAQUE_KSF_MEMORY_KIB=8
 OXICLOUD_AUTH_OPAQUE_KSF_ITERATIONS=1
 OXICLOUD_AUTH_OPAQUE_KSF_PARALLELISM=1
 
+# DPoP (RFC 9449) — required mode surfaces every verifier /
+# nonce / replay bug as a hard 401 (opportunistic would swallow
+# some cases as warnings). Safe today because unbound sessions —
+# `session.dpop_jkt IS NULL`, which is where the test admin's
+# legacy-login lands — are still exempted at the middleware; the
+# session-level enforcement flip is Gate 9. Once that arrives,
+# every bind-time downgrade path also gets caught here without
+# a config change. `dpop-hurl-helper` needs this on or the
+# middleware is a pass-through and its scenarios all silently 200.
+OXICLOUD_DPOP_MODE=required
+