diff --git a/.github/workflows/xtest.yml b/.github/workflows/xtest.yml
index 48ed7fea..1f5b484b 100644
--- a/.github/workflows/xtest.yml
+++ b/.github/workflows/xtest.yml
@@ -297,13 +297,14 @@ jobs:
       ######## SPIN UP PLATFORM BACKEND #############
       - name: Check out and start up platform with deps/containers
         id: run-platform
-        uses: opentdf/platform/test/start-up-with-containers@11af44a5d4826ed281bf2e0e4e31d6ff6154b393  # pqc-enabled
+        uses: opentdf/platform/test/start-up-with-containers@8ccc608d2947f7f868d63e3741d3e78dc0ee88ce  # DSPX-3397-platform-go-sdk
         with:
           platform-ref: ${{ fromJSON(needs.resolve-versions.outputs.platform-tag-to-sha)[matrix.platform-tag] }}
           ec-tdf-enabled: true
           extra-keys: ${{ steps.load-extra-keys.outputs.EXTRA_KEYS }}
           log-type: json
           pqc-enabled: ${{ steps.pqc-check.outputs.supported == 'true' }}
+          dpop-challenge-enabled: true
 
       - name: Install uv
         uses: astral-sh/setup-uv@fac544c07dec837d0ccb6301d7b5580bf5edae39 # v8.2.0
@@ -591,7 +592,7 @@ jobs:
       - name: Start additional kas
         id: kas-alpha
         if: ${{ steps.multikas.outputs.supported == 'true' }}
-        uses: opentdf/platform/test/start-additional-kas@11af44a5d4826ed281bf2e0e4e31d6ff6154b393  # pqc-enabled
+        uses: opentdf/platform/test/start-additional-kas@8ccc608d2947f7f868d63e3741d3e78dc0ee88ce  # DSPX-3397-platform-go-sdk: require_nonce on additional KAS
         with:
           ec-tdf-enabled: true
           kas-name: alpha
@@ -599,11 +600,12 @@ jobs:
           log-type: json
           pqc-enabled: ${{ steps.pqc-check.outputs.supported == 'true' }}
           root-key: ${{ steps.km-check.outputs.root_key }}
+          dpop-challenge-enabled: true
 
       - name: Start additional kas
         id: kas-beta
         if: ${{ steps.multikas.outputs.supported == 'true' }}
-        uses: opentdf/platform/test/start-additional-kas@11af44a5d4826ed281bf2e0e4e31d6ff6154b393  # pqc-enabled
+        uses: opentdf/platform/test/start-additional-kas@8ccc608d2947f7f868d63e3741d3e78dc0ee88ce  # DSPX-3397-platform-go-sdk: require_nonce on additional KAS
         with:
           ec-tdf-enabled: true
           kas-name: beta
@@ -611,11 +613,12 @@ jobs:
           log-type: json
           pqc-enabled: ${{ steps.pqc-check.outputs.supported == 'true' }}
           root-key: ${{ steps.km-check.outputs.root_key }}
+          dpop-challenge-enabled: true
 
       - name: Start additional kas
         id: kas-gamma
         if: ${{ steps.multikas.outputs.supported == 'true' }}
-        uses: opentdf/platform/test/start-additional-kas@11af44a5d4826ed281bf2e0e4e31d6ff6154b393  # pqc-enabled
+        uses: opentdf/platform/test/start-additional-kas@8ccc608d2947f7f868d63e3741d3e78dc0ee88ce  # DSPX-3397-platform-go-sdk: require_nonce on additional KAS
         with:
           ec-tdf-enabled: true
           kas-name: gamma
@@ -623,11 +626,12 @@ jobs:
           log-type: json
           pqc-enabled: ${{ steps.pqc-check.outputs.supported == 'true' }}
           root-key: ${{ steps.km-check.outputs.root_key }}
+          dpop-challenge-enabled: true
 
       - name: Start additional kas
         id: kas-delta
         if: ${{ steps.multikas.outputs.supported == 'true' }}
-        uses: opentdf/platform/test/start-additional-kas@11af44a5d4826ed281bf2e0e4e31d6ff6154b393  # pqc-enabled
+        uses: opentdf/platform/test/start-additional-kas@8ccc608d2947f7f868d63e3741d3e78dc0ee88ce  # DSPX-3397-platform-go-sdk: require_nonce on additional KAS
         with:
           ec-tdf-enabled: true
           kas-port: 8484
@@ -635,11 +639,12 @@ jobs:
           log-type: json
           pqc-enabled: ${{ steps.pqc-check.outputs.supported == 'true' }}
           root-key: ${{ steps.km-check.outputs.root_key }}
+          dpop-challenge-enabled: true
 
       - name: Start additional KM kas (km1)
         id: kas-km1
         if: ${{ steps.multikas.outputs.supported == 'true' }}
-        uses: opentdf/platform/test/start-additional-kas@11af44a5d4826ed281bf2e0e4e31d6ff6154b393  # pqc-enabled
+        uses: opentdf/platform/test/start-additional-kas@8ccc608d2947f7f868d63e3741d3e78dc0ee88ce  # DSPX-3397-platform-go-sdk: require_nonce on additional KAS
         with:
           ec-tdf-enabled: true
           key-management: ${{ steps.km-check.outputs.supported }}
@@ -648,11 +653,12 @@ jobs:
           log-type: json
           pqc-enabled: ${{ steps.pqc-check.outputs.supported == 'true' }}
           root-key: ${{ steps.km-check.outputs.root_key }}
+          dpop-challenge-enabled: true
 
       - name: Start additional KM kas (km2)
         id: kas-km2
         if: ${{ steps.multikas.outputs.supported == 'true' }}
-        uses: opentdf/platform/test/start-additional-kas@11af44a5d4826ed281bf2e0e4e31d6ff6154b393  # pqc-enabled
+        uses: opentdf/platform/test/start-additional-kas@8ccc608d2947f7f868d63e3741d3e78dc0ee88ce  # DSPX-3397-platform-go-sdk: require_nonce on additional KAS
         with:
           ec-tdf-enabled: true
           kas-name: km2
@@ -661,6 +667,7 @@ jobs:
           log-type: json
           pqc-enabled: ${{ steps.pqc-check.outputs.supported == 'true' }}
           root-key: ${{ steps.km-check.outputs.root_key }}
+          dpop-challenge-enabled: true
 
       - name: Run attribute based configuration tests
         if: ${{ steps.multikas.outputs.supported == 'true' }}
diff --git a/xtest/sdk/java/cli.sh b/xtest/sdk/java/cli.sh
index cece9630..d8013a08 100755
--- a/xtest/sdk/java/cli.sh
+++ b/xtest/sdk/java/cli.sh
@@ -42,6 +42,29 @@ else
   exit 1
 fi
 
+# Cache `java -jar cmdline.jar help [...]` output to avoid paying JVM startup
+# (typically 150-500ms) for the capability probes on every encrypt/decrypt.
+# Keyed by the jar's mtime so a reinstall invalidates the cache. stderr is
+# discarded to keep JVM warnings (reflective-access, agent notices) out of logs.
+jar_help() {
+  local jar="$SCRIPT_DIR/cmdline.jar"
+  local mtime
+  mtime=$(stat -c %Y "$jar" 2>/dev/null || stat -f %m "$jar" 2>/dev/null || echo 0)
+  local key
+  key=$(printf '%s' "$*" | tr -c 'a-zA-Z0-9' '_')
+  local uid
+  uid=$(id -u 2>/dev/null || echo default)
+  local cache="${TMPDIR:-/tmp}/xtest-java-help-${uid}-${mtime}-${key}"
+  if [[ ! -f "$cache" ]]; then
+    # Write to a process-unique temp file, then rename: concurrent xdist
+    # workers see either no cache or the complete file, never a partial read.
+    local tmp="${cache}.$$"
+    java -jar "$jar" help "$@" >"$tmp" 2>/dev/null
+    mv -f "$tmp" "$cache"
+  fi
+  cat "$cache"
+}
+
 if [ "$1" == "supports" ]; then
   case "$2" in
     autoconfigure | ns_grants)
@@ -118,8 +141,8 @@ if [ "$1" == "supports" ]; then
       exit $?
       ;;
     dpop_nonce_challenge)
-      echo "dpop_nonce_challenge not supported"
-      exit 1
+      java -jar "$SCRIPT_DIR"/cmdline.jar supports dpop_nonce_challenge
+      exit $?
       ;;
     *)
       echo "Unknown feature: $2"
@@ -135,7 +158,7 @@ args=(
 )
 
 # when we added support for KAS allowlist, we changed the platform endpoint format to require scheme
-if java -jar "$SCRIPT_DIR"/cmdline.jar help decrypt | grep kas-allowlist; then
+if jar_help decrypt | grep -q kas-allowlist; then
   args+=("--platform-endpoint=$PLATFORMURL")
 else
   args+=("--platform-endpoint=$PLATFORMENDPOINT")
@@ -197,5 +220,9 @@ if [ -n "$XT_WITH_TARGET_MODE" ]; then
   args+=(--with-target-mode "$XT_WITH_TARGET_MODE")
 fi
 
+if jar_help | grep -q -- '--verbose'; then
+  args+=(--verbose)
+fi
+
 echo java -jar "$SCRIPT_DIR"/cmdline.jar "${args[@]}" --file="$2" ">" "$3"
 java -jar "$SCRIPT_DIR"/cmdline.jar "${args[@]}" --file="$2" >"$3"
diff --git a/xtest/sdk/js/cli.sh b/xtest/sdk/js/cli.sh
index d3160ca3..11c1dfe1 100755
--- a/xtest/sdk/js/cli.sh
+++ b/xtest/sdk/js/cli.sh
@@ -18,6 +18,10 @@
 #  XT_WITH_ATTRIBUTES [string] - Attributes to be used for encryption
 #  XT_WITH_MIME_TYPE [string] - MIME type for the encrypted file
 #  XT_WITH_TARGET_MODE [string] - Target spec mode for the encrypted file
+#  XT_WITH_DPOP [string] - Enable DPoP token binding; value selects algorithm (e.g. ES256)
+#  XT_WITH_DPOP_KEY [string] - Path to PEM-encoded PKCS8 private key for DPoP signing
+#  CLIENTID [string] - Override OIDC client ID (default: opentdf)
+#  CLIENTSECRET [string] - Override OIDC client secret (default: secret)
 #
 SCRIPT_DIR=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" &>/dev/null && pwd)
 
@@ -124,9 +128,17 @@ if [ "$XTEST_DIR" = "/" ]; then
   exit 1
 fi
 
+# Capture any caller-set overrides before test.env unconditionally resets them.
+_pre_clientid="${CLIENTID:-}"
+_pre_clientsecret="${CLIENTSECRET:-}"
+
 # shellcheck disable=SC1091
 source "$XTEST_DIR"/test.env
 
+# Restore caller overrides (e.g. from pytest monkeypatch for DPoP client).
+[[ -n "$_pre_clientid" ]] && CLIENTID="$_pre_clientid"
+[[ -n "$_pre_clientsecret" ]] && CLIENTSECRET="$_pre_clientsecret"
+
 src_file=$(realpath "$2")
 dst_file=$(realpath "$(dirname "$3")")/$(basename "$3")
 
@@ -134,9 +146,16 @@ args=(
   --output "$dst_file"
   --kasEndpoint "$KASURL"
   --oidcEndpoint "$KCFULLURL"
-  --auth opentdf:secret
+  --auth "${CLIENTID:-opentdf}:${CLIENTSECRET:-secret}"
 )
 
+if [ -n "$XT_WITH_DPOP" ]; then
+  args+=(--dpop "$XT_WITH_DPOP")
+fi
+if [ -n "$XT_WITH_DPOP_KEY" ]; then
+  args+=(--dpop-key "$XT_WITH_DPOP_KEY")
+fi
+
 args+=(--containerType tdf3)
 
 if [ -n "$XT_WITH_ATTRIBUTES" ]; then
@@ -185,6 +204,24 @@ if ! cd "$SCRIPT_DIR"; then
   exit 1
 fi
 
+# Echo a CLI invocation with the --auth secret masked, so CI logs never capture
+# client credentials. The real (unmasked) args are still used for execution.
+echo_redacted() {
+  local out=() a mask_next=0
+  for a in "$@"; do
+    if [[ "$mask_next" == 1 ]]; then
+      out+=("${a%%:*}:***")
+      mask_next=0
+    elif [[ "$a" == "--auth" ]]; then
+      out+=("$a")
+      mask_next=1
+    else
+      out+=("$a")
+    fi
+  done
+  echo "${out[@]}"
+}
+
 if [ "$1" == "encrypt" ]; then
   if npx $CTL help | grep autoconfigure; then
     args+=(--policyEndpoint "$PLATFORMURL" --autoconfigure true)
@@ -205,7 +242,7 @@ if [ "$1" == "encrypt" ]; then
     args+=(--tdfSpecVersion "$XT_WITH_TARGET_MODE")
   fi
 
-  echo npx $CTL encrypt "$src_file" "${args[@]}"
+  echo_redacted npx $CTL encrypt "$src_file" "${args[@]}"
   npx $CTL encrypt "$src_file" "${args[@]}"
 elif [ "$1" == "decrypt" ]; then
   if [ "$XT_WITH_VERIFY_ASSERTIONS" == 'false' ]; then
@@ -227,7 +264,7 @@ elif [ "$1" == "decrypt" ]; then
     args+=(--ignoreAllowList)
   fi
 
-  echo npx $CTL decrypt "$src_file" "${args[@]}"
+  echo_redacted npx $CTL decrypt "$src_file" "${args[@]}"
   npx $CTL decrypt "$src_file" "${args[@]}"
 else
   echo "Incorrect argument provided"
diff --git a/xtest/test_dpop.py b/xtest/test_dpop.py
index 085f71fc..18844774 100644
--- a/xtest/test_dpop.py
+++ b/xtest/test_dpop.py
@@ -305,6 +305,37 @@ def _post_rewrap(
     )
 
 
+def _post_rewrap_with_nonce_retry(
+    call: RewrapCall,
+    key: DPoPKey,
+    *,
+    access_token: str,
+    auth_scheme: str = "DPoP",
+) -> requests.Response:
+    """POST a rewrap, transparently satisfying a `require_nonce` challenge.
+
+    Mints a fresh DPoP proof (no nonce) and sends it. If the KAS replies with a
+    `401` carrying a `DPoP-Nonce` header (the `use_dpop_nonce` challenge), the
+    proof is re-minted with that nonce and the request is retried once, keeping
+    the same `auth_scheme`. This makes callers agnostic to whether
+    `require_nonce` is enabled on the target KAS: with it off the first request
+    is returned as-is; with it on the second (nonce-bearing) request is.
+    """
+    proof = key.sign_dpop_proof(htm="POST", htu=call.url, access_token=access_token)
+    response = _post_rewrap(
+        call, access_token=access_token, dpop_proof=proof, auth_scheme=auth_scheme
+    )
+    nonce = response.headers.get("DPoP-Nonce")
+    if response.status_code == 401 and nonce:
+        proof = key.sign_dpop_proof(
+            htm="POST", htu=call.url, access_token=access_token, nonce=nonce
+        )
+        response = _post_rewrap(
+            call, access_token=access_token, dpop_proof=proof, auth_scheme=auth_scheme
+        )
+    return response
+
+
 def _assert_unauthorized(response: requests.Response) -> None:
     assert response.status_code == 401, response.text
     # Confirm the rejection is actually a DPoP-related challenge so a 401
@@ -323,9 +354,11 @@ def _skip_unless_dpop_enabled(encrypt_sdk: tdfs.SDK, in_focus: set[tdfs.SDK]) ->
 
 @pytest.fixture(autouse=True)
 def _dpop_client_env(monkeypatch: pytest.MonkeyPatch) -> None:
-    # SDK CLI shims read CLIENTID from the environment; tests in this module
-    # must use the DPoP-bound client provisioned by `service provision keycloak`.
+    # SDK CLI shims read CLIENTID/XT_WITH_DPOP from the environment; tests in
+    # this module must use the DPoP-bound client provisioned by
+    # `service provision keycloak` and enable DPoP proof generation.
     monkeypatch.setenv("CLIENTID", "opentdf-dpop")
+    monkeypatch.setenv("XT_WITH_DPOP", "ES256")
 
 
 def test_dpop_happy_path_roundtrip(
@@ -426,16 +459,14 @@ def test_dpop_bearer_scheme_warns_but_accepted_for_dpop_token(
     dpop_access = _get_dpop_access_token()
     rewrap_call = _signed_rewrap_request(ct_file, dpop_access.key)
 
-    bearer_proof = dpop_access.key.sign_dpop_proof(
-        htm="POST",
-        htu=rewrap_call.url,
-        access_token=dpop_access.token,
-    )
+    # Both calls go through the nonce-retry helper so the test passes whether or
+    # not the target KAS has `require_nonce` enabled: when it is, the lenient
+    # accept (and the WARN) only happen after the nonce challenge is satisfied.
     mark = audit_logs.mark("before_bearer_scheme_request")
-    bearer_response = _post_rewrap(
+    bearer_response = _post_rewrap_with_nonce_retry(
         rewrap_call,
+        dpop_access.key,
         access_token=dpop_access.token,
-        dpop_proof=bearer_proof,
         auth_scheme="Bearer",
     )
 
@@ -447,16 +478,10 @@ def test_dpop_bearer_scheme_warns_but_accepted_for_dpop_token(
     )
 
     # Compliant path control: same proof key, same token, just the right scheme.
-    # Distinct jti via fresh proof so the server's replay cache doesn't reject it.
-    dpop_proof = dpop_access.key.sign_dpop_proof(
-        htm="POST",
-        htu=rewrap_call.url,
-        access_token=dpop_access.token,
-    )
-    dpop_response = _post_rewrap(
+    dpop_response = _post_rewrap_with_nonce_retry(
         rewrap_call,
+        dpop_access.key,
         access_token=dpop_access.token,
-        dpop_proof=dpop_proof,
         auth_scheme="DPoP",
     )
     assert dpop_response.status_code == 200, dpop_response.text