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diff --git a/services/common/hawkrequest.sys.mjs b/services/common/hawkrequest.sys.mjs
new file mode 100644
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+++ b/services/common/hawkrequest.sys.mjs
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import { Log } from "resource://gre/modules/Log.sys.mjs";
+
+import { RESTRequest } from "resource://services-common/rest.sys.mjs";
+import { CommonUtils } from "resource://services-common/utils.sys.mjs";
+import { Credentials } from "resource://gre/modules/Credentials.sys.mjs";
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  CryptoUtils: "resource://services-crypto/utils.sys.mjs",
+});
+
+/**
+ * Single-use HAWK-authenticated HTTP requests to RESTish resources.
+ *
+ * @param uri
+ *        (String) URI for the RESTRequest constructor
+ *
+ * @param credentials
+ *        (Object) Optional credentials for computing HAWK authentication
+ *        header.
+ *
+ * @param payloadObj
+ *        (Object) Optional object to be converted to JSON payload
+ *
+ * @param extra
+ *        (Object) Optional extra params for HAWK header computation.
+ *        Valid properties are:
+ *
+ *          now:                 <current time in milliseconds>,
+ *          localtimeOffsetMsec: <local clock offset vs server>,
+ *          headers:             <An object with header/value pairs to be sent
+ *                                as headers on the request>
+ *
+ * extra.localtimeOffsetMsec is the value in milliseconds that must be added to
+ * the local clock to make it agree with the server's clock.  For instance, if
+ * the local clock is two minutes ahead of the server, the time offset in
+ * milliseconds will be -120000.
+ */
+
+export var HAWKAuthenticatedRESTRequest = function HawkAuthenticatedRESTRequest(
+  uri,
+  credentials,
+  extra = {}
+) {
+  RESTRequest.call(this, uri);
+
+  this.credentials = credentials;
+  this.now = extra.now || Date.now();
+  this.localtimeOffsetMsec = extra.localtimeOffsetMsec || 0;
+  this._log.trace(
+    "local time, offset: " + this.now + ", " + this.localtimeOffsetMsec
+  );
+  this.extraHeaders = extra.headers || {};
+
+  // Expose for testing
+  this._intl = getIntl();
+};
+
+HAWKAuthenticatedRESTRequest.prototype = {
+  async dispatch(method, data) {
+    let contentType = "text/plain";
+    if (method == "POST" || method == "PUT" || method == "PATCH") {
+      contentType = "application/json";
+    }
+    if (this.credentials) {
+      let options = {
+        now: this.now,
+        localtimeOffsetMsec: this.localtimeOffsetMsec,
+        credentials: this.credentials,
+        payload: (data && JSON.stringify(data)) || "",
+        contentType,
+      };
+      let header = await lazy.CryptoUtils.computeHAWK(
+        this.uri,
+        method,
+        options
+      );
+      this.setHeader("Authorization", header.field);
+    }
+
+    for (let header in this.extraHeaders) {
+      this.setHeader(header, this.extraHeaders[header]);
+    }
+
+    this.setHeader("Content-Type", contentType);
+
+    this.setHeader("Accept-Language", this._intl.accept_languages);
+
+    return super.dispatch(method, data);
+  },
+};
+
+Object.setPrototypeOf(
+  HAWKAuthenticatedRESTRequest.prototype,
+  RESTRequest.prototype
+);
+
+/**
+ * Generic function to derive Hawk credentials.
+ *
+ * Hawk credentials are derived using shared secrets, which depend on the token
+ * in use.
+ *
+ * @param tokenHex
+ *        The current session token encoded in hex
+ * @param context
+ *        A context for the credentials. A protocol version will be prepended
+ *        to the context, see Credentials.keyWord for more information.
+ * @param size
+ *        The size in bytes of the expected derived buffer,
+ *        defaults to 3 * 32.
+ * @return credentials
+ *        Returns an object:
+ *        {
+ *          id: the Hawk id (from the first 32 bytes derived)
+ *          key: the Hawk key (from bytes 32 to 64)
+ *          extra: size - 64 extra bytes (if size > 64)
+ *        }
+ */
+export async function deriveHawkCredentials(tokenHex, context, size = 96) {
+  let token = CommonUtils.hexToBytes(tokenHex);
+  let out = await lazy.CryptoUtils.hkdfLegacy(
+    token,
+    undefined,
+    Credentials.keyWord(context),
+    size
+  );
+
+  let result = {
+    key: out.slice(32, 64),
+    id: CommonUtils.bytesAsHex(out.slice(0, 32)),
+  };
+  if (size > 64) {
+    result.extra = out.slice(64);
+  }
+
+  return result;
+}
+
+// With hawk request, we send the user's accepted-languages with each request.
+// To keep the number of times we read this pref at a minimum, maintain the
+// preference in a stateful object that notices and updates itself when the
+// pref is changed.
+function Intl() {
+  // We won't actually query the pref until the first time we need it
+  this._accepted = "";
+  this._everRead = false;
+  this.init();
+}
+
+Intl.prototype = {
+  init() {
+    Services.prefs.addObserver("intl.accept_languages", this);
+  },
+
+  uninit() {
+    Services.prefs.removeObserver("intl.accept_languages", this);
+  },
+
+  observe(subject, topic, data) {
+    this.readPref();
+  },
+
+  readPref() {
+    this._everRead = true;
+    try {
+      this._accepted = Services.prefs.getComplexValue(
+        "intl.accept_languages",
+        Ci.nsIPrefLocalizedString
+      ).data;
+    } catch (err) {
+      let log = Log.repository.getLogger("Services.Common.RESTRequest");
+      log.error("Error reading intl.accept_languages pref", err);
+    }
+  },
+
+  get accept_languages() {
+    if (!this._everRead) {
+      this.readPref();
+    }
+    return this._accepted;
+  },
+};
+
+// Singleton getter for Intl, creating an instance only when we first need it.
+var intl = null;
+function getIntl() {
+  if (!intl) {
+    intl = new Intl();
+  }
+  return intl;
+}