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diff --git a/toolkit/modules/CertUtils.sys.mjs b/toolkit/modules/CertUtils.sys.mjs
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+++ b/toolkit/modules/CertUtils.sys.mjs
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+const Ce = Components.Exception;
+
+/**
+ * Reads a set of expected certificate attributes from preferences. The returned
+ * array can be passed to validateCert or checkCert to validate that a
+ * certificate matches the expected attributes. The preferences should look like
+ * this:
+ *   prefix.1.attribute1
+ *   prefix.1.attribute2
+ *   prefix.2.attribute1
+ *   etc.
+ * Each numeric branch contains a set of required attributes for a single
+ * certificate. Having multiple numeric branches means that multiple
+ * certificates would be accepted by validateCert.
+ *
+ * @param  aPrefBranch
+ *         The prefix for all preferences, should end with a ".".
+ * @return An array of JS objects with names / values corresponding to the
+ *         expected certificate's attribute names / values.
+ */
+function readCertPrefs(aPrefBranch) {
+  if (!Services.prefs.getBranch(aPrefBranch).getChildList("").length) {
+    return null;
+  }
+
+  let certs = [];
+  let counter = 1;
+  while (true) {
+    let prefBranchCert = Services.prefs.getBranch(aPrefBranch + counter + ".");
+    let prefCertAttrs = prefBranchCert.getChildList("");
+    if (!prefCertAttrs.length) {
+      break;
+    }
+
+    let certAttrs = {};
+    for (let prefCertAttr of prefCertAttrs) {
+      certAttrs[prefCertAttr] = prefBranchCert.getCharPref(prefCertAttr);
+    }
+
+    certs.push(certAttrs);
+    counter++;
+  }
+
+  return certs;
+}
+
+/**
+ * Verifies that an nsIX509Cert matches the expected certificate attribute
+ * values.
+ *
+ * @param  aCertificate
+ *         The nsIX509Cert to compare to the expected attributes.
+ * @param  aCerts
+ *         An array of JS objects with names / values corresponding to the
+ *         expected certificate's attribute names / values. If this is null or
+ *         an empty array then no checks are performed.
+ * @throws NS_ERROR_ILLEGAL_VALUE if a certificate attribute name from the
+ *         aCerts param does not exist or the value for a certificate attribute
+ *         from the aCerts param is different than the expected value or
+ *         aCertificate wasn't specified and aCerts is not null or an empty
+ *         array.
+ */
+function validateCert(aCertificate, aCerts) {
+  // If there are no certificate requirements then just exit
+  if (!aCerts || !aCerts.length) {
+    return;
+  }
+
+  if (!aCertificate) {
+    const missingCertErr = "A required certificate was not present.";
+    console.error(missingCertErr);
+    throw new Ce(missingCertErr, Cr.NS_ERROR_ILLEGAL_VALUE);
+  }
+
+  var errors = [];
+  for (var i = 0; i < aCerts.length; ++i) {
+    var error = false;
+    var certAttrs = aCerts[i];
+    for (var name in certAttrs) {
+      if (!(name in aCertificate)) {
+        error = true;
+        errors.push(
+          "Expected attribute '" + name + "' not present in certificate."
+        );
+        break;
+      }
+      if (aCertificate[name] != certAttrs[name]) {
+        error = true;
+        errors.push(
+          "Expected certificate attribute '" +
+            name +
+            "' " +
+            "value incorrect, expected: '" +
+            certAttrs[name] +
+            "', got: '" +
+            aCertificate[name] +
+            "'."
+        );
+        break;
+      }
+    }
+
+    if (!error) {
+      break;
+    }
+  }
+
+  if (error) {
+    errors.forEach(Cu.reportError.bind(Cu));
+    const certCheckErr =
+      "Certificate checks failed. See previous errors for details.";
+    console.error(certCheckErr);
+    throw new Ce(certCheckErr, Cr.NS_ERROR_ILLEGAL_VALUE);
+  }
+}
+
+/**
+ * Checks if the connection must be HTTPS and if so, only allows built-in
+ * certificates and validates application specified certificate attribute
+ * values.
+ * See bug 340198 and bug 544442.
+ *
+ * @param  aChannel
+ *         The nsIChannel that will have its certificate checked.
+ * @param  aAllowNonBuiltInCerts (optional)
+ *         When true certificates that aren't builtin are allowed. When false
+ *         or not specified the certificate must be a builtin certificate.
+ * @param  aCerts (optional)
+ *         An array of JS objects with names / values corresponding to the
+ *         channel's expected certificate's attribute names / values. If it
+ *         isn't null or not specified the the scheme for the channel's
+ *         originalURI must be https.
+ * @throws NS_ERROR_UNEXPECTED if a certificate is expected and the URI scheme
+ *         is not https.
+ *         NS_ERROR_ILLEGAL_VALUE if a certificate attribute name from the
+ *         aCerts param does not exist or the value for a certificate attribute
+ *         from the aCerts  param is different than the expected value.
+ *         NS_ERROR_ABORT if the certificate issuer is not built-in.
+ */
+function checkCert(aChannel, aAllowNonBuiltInCerts, aCerts) {
+  if (!aChannel.originalURI.schemeIs("https")) {
+    // Require https if there are certificate values to verify
+    if (aCerts) {
+      throw new Ce(
+        "SSL is required and URI scheme is not https.",
+        Cr.NS_ERROR_UNEXPECTED
+      );
+    }
+    return;
+  }
+
+  let secInfo = aChannel.securityInfo;
+  let cert = secInfo.serverCert;
+
+  validateCert(cert, aCerts);
+
+  if (aAllowNonBuiltInCerts === true) {
+    return;
+  }
+
+  let issuerCert = null;
+  if (secInfo.succeededCertChain.length) {
+    issuerCert =
+      secInfo.succeededCertChain[secInfo.succeededCertChain.length - 1];
+  }
+
+  const certNotBuiltInErr = "Certificate issuer is not built-in.";
+  if (!issuerCert) {
+    throw new Ce(certNotBuiltInErr, Cr.NS_ERROR_ABORT);
+  }
+
+  if (!issuerCert.isBuiltInRoot) {
+    throw new Ce(certNotBuiltInErr, Cr.NS_ERROR_ABORT);
+  }
+}
+
+/**
+ * This class implements nsIChannelEventSink. Its job is to perform extra checks
+ * on the certificates used for some connections when those connections
+ * redirect.
+ *
+ * @param  aAllowNonBuiltInCerts (optional)
+ *         When true certificates that aren't builtin are allowed. When false
+ *         or not specified the certificate must be a builtin certificate.
+ */
+function BadCertHandler(aAllowNonBuiltInCerts) {
+  this.allowNonBuiltInCerts = aAllowNonBuiltInCerts;
+}
+BadCertHandler.prototype = {
+  // nsIChannelEventSink
+  asyncOnChannelRedirect(oldChannel, newChannel, flags, callback) {
+    if (this.allowNonBuiltInCerts) {
+      callback.onRedirectVerifyCallback(Cr.NS_OK);
+      return;
+    }
+
+    // make sure the certificate of the old channel checks out before we follow
+    // a redirect from it.  See bug 340198.
+    // Don't call checkCert for internal redirects. See bug 569648.
+    if (!(flags & Ci.nsIChannelEventSink.REDIRECT_INTERNAL)) {
+      checkCert(oldChannel);
+    }
+
+    callback.onRedirectVerifyCallback(Cr.NS_OK);
+  },
+
+  // nsIInterfaceRequestor
+  getInterface(iid) {
+    return this.QueryInterface(iid);
+  },
+
+  // nsISupports
+  QueryInterface: ChromeUtils.generateQI([
+    "nsIChannelEventSink",
+    "nsIInterfaceRequestor",
+  ]),
+};
+
+export var CertUtils = {
+  BadCertHandler,
+  checkCert,
+  readCertPrefs,
+  validateCert,
+};