.../LibraryDefinitionMissingLicenseException.php   | 15 +++++
 core/lib/Drupal/Core/Asset/LibraryDiscovery.php    |  6 ++
 core/modules/system/system.routing.yml             |  8 ---
 .../Tests/Core/Asset/LibraryDiscoveryTest.php      | 46 ++++++++++++--
 .../library_test_files/licenses.libraries.yml      | 72 ++++++++++++++++++++++
 .../licenses_missing_information.libraries.yml     |  9 +++
 6 files changed, 142 insertions(+), 14 deletions(-)

diff --git a/core/lib/Drupal/Core/Asset/Exception/LibraryDefinitionMissingLicenseException.php b/core/lib/Drupal/Core/Asset/Exception/LibraryDefinitionMissingLicenseException.php
new file mode 100644
index 0000000..2ed2c70
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/Exception/LibraryDefinitionMissingLicenseException.php
@@ -0,0 +1,15 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\Exception\LibraryDefinitionMissingLicenseException.
+ */
+
+namespace Drupal\Core\Asset\Exception;
+
+/**
+ * Defines a custom exception if a library has a remote but no license.
+ */
+class LibraryDefinitionMissingLicenseException extends \RuntimeException {
+
+}
diff --git a/core/lib/Drupal/Core/Asset/LibraryDiscovery.php b/core/lib/Drupal/Core/Asset/LibraryDiscovery.php
index a5c477c..d640008 100644
--- a/core/lib/Drupal/Core/Asset/LibraryDiscovery.php
+++ b/core/lib/Drupal/Core/Asset/LibraryDiscovery.php
@@ -11,6 +11,7 @@
 use Drupal\Component\Serialization\Exception\InvalidDataTypeException;
 use Drupal\Core\Asset\Exception\IncompleteLibraryDefinitionException;
 use Drupal\Core\Asset\Exception\InvalidLibraryFileException;
+use Drupal\Core\Asset\Exception\LibraryDefinitionMissingLicenseException;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
@@ -174,6 +175,11 @@ protected function buildLibrariesByExtension($extension) {
         }
       }
 
+      // If this is a 3rd party library, the license info is required.
+      if (isset($library['remote']) && !isset($library['license'])) {
+        throw new LibraryDefinitionMissingLicenseException(sprintf("Missing license information in library definition for '%s' in %s: it has a remote, but no license.", $id, $library_file));
+      }
+
       // Assign Drupal's license to libraries that don't have license info.
       if (!isset($library['license'])) {
         $library['license'] = array(
diff --git a/core/modules/system/system.routing.yml b/core/modules/system/system.routing.yml
index dadbf74..13019c2 100644
--- a/core/modules/system/system.routing.yml
+++ b/core/modules/system/system.routing.yml
@@ -408,11 +408,3 @@ system.batch_page.json:
 
 system.update:
   path: '/core/update.php'
-
-system.javascript_license_web_labels:
-  path: '/system/jslicense'
-  defaults:
-    _content: '\Drupal\system\Controller\AssetLicenseInfoController::jslicense'
-    _title: 'JavaScript license information'
-  requirements:
-    _access: 'TRUE'
diff --git a/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryTest.php b/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryTest.php
index 37975d7..d53f1fc 100644
--- a/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryTest.php
+++ b/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryTest.php
@@ -32,6 +32,9 @@
 /**
  * Tests the library discovery.
  *
+ *
+ * @group kak
+ *
  * @coversDefaultClass \Drupal\Core\Asset\LibraryDiscovery
  */
 class LibraryDiscoveryTest extends UnitTestCase {
@@ -376,6 +379,37 @@ public function testLibraryWithDataTypes() {
   }
 
   /**
+   * Tests that an exception is thrown when license is missing when 3rd party.
+   *
+   * @expectedException \Drupal\Core\Asset\Exception\LibraryDefinitionMissingLicenseException
+   * @expectedExceptionMessage Missing license information in library definition for 'no-license-info-but-remote' in core/tests/Drupal/Tests/Core/Asset/library_test_files/licenses_missing_information.libraries.yml: it has a remote, but no license.
+   *
+   * @covers ::buildLibrariesByExtension()
+   */
+  public function testLibraryWithMissingLicense() {
+    $this->moduleHandler->expects($this->atLeastOnce())
+      ->method('moduleExists')
+      ->with('licenses_missing_information')
+      ->will($this->returnValue(TRUE));
+
+    $path = __DIR__ . '/library_test_files';
+    $path = substr($path, strlen(DRUPAL_ROOT) + 1);
+    $this->libraryDiscovery->setPaths('module', 'licenses_missing_information', $path);
+
+    // For libraries without license info, the default license is applied.
+    $library = $this->libraryDiscovery->getLibraryByName('licenses_missing_information', 'no-license-info-but-remote');
+    $this->assertCount(1, $library['css']);
+    $this->assertCount(1, $library['js']);
+    $this->assertTrue(isset($library['license']));
+    $default_license = array(
+      'name' => 'GNU-GPL-2.0-or-later',
+      'url' => 'https://drupal.org/licensing/faq',
+      'gpl-compatible' => TRUE,
+    );
+    $this->assertEquals($library['license'], $default_license);
+  }
+
+  /**
    * Tests a library with various licenses, some GPL-compatible, some not.
    *
    * @covers ::buildLibrariesByExtension()
@@ -400,7 +434,7 @@ public function testLibraryWithLicenses() {
       'url' => 'https://drupal.org/licensing/faq',
       'gpl-compatible' => TRUE,
     );
-    $this->assertEquals($library['license'], $default_license, 'Default license is applied.');
+    $this->assertEquals($library['license'], $default_license);
 
     // GPL2-licensed libraries.
     $library = $this->libraryDiscovery->getLibraryByName('licenses', 'gpl2');
@@ -411,7 +445,7 @@ public function testLibraryWithLicenses() {
       'url' => 'https://url-to-gpl2-license',
       'gpl-compatible' => TRUE,
     );
-    $this->assertEquals($library['license'], $expected_license, 'Expected license metadata found.');
+    $this->assertEquals($library['license'], $expected_license);
 
     // MIT-licensed libraries.
     $library = $this->libraryDiscovery->getLibraryByName('licenses', 'mit');
@@ -422,7 +456,7 @@ public function testLibraryWithLicenses() {
       'url' => 'https://url-to-mit-license',
       'gpl-compatible' => TRUE,
     );
-    $this->assertEquals($library['license'], $expected_license, 'Expected license metadata found.');
+    $this->assertEquals($library['license'], $expected_license);
 
     // Libraries in the Public Domain.
     $library = $this->libraryDiscovery->getLibraryByName('licenses', 'public-domain');
@@ -433,7 +467,7 @@ public function testLibraryWithLicenses() {
       'url' => 'https://url-to-public-domain-license',
       'gpl-compatible' => TRUE,
     );
-    $this->assertEquals($library['license'], $expected_license, 'Expected license metadata found.');
+    $this->assertEquals($library['license'], $expected_license);
 
     // Apache-licensed libraries.
     $library = $this->libraryDiscovery->getLibraryByName('licenses', 'apache');
@@ -444,7 +478,7 @@ public function testLibraryWithLicenses() {
       'url' => 'https://url-to-apache-license',
       'gpl-compatible' => FALSE,
     );
-    $this->assertEquals($library['license'], $expected_license, 'Expected license metadata found.');
+    $this->assertEquals($library['license'], $expected_license);
 
     // Copyrighted libraries.
     $library = $this->libraryDiscovery->getLibraryByName('licenses', 'copyright');
@@ -454,7 +488,7 @@ public function testLibraryWithLicenses() {
       'name' => '© Some company',
       'gpl-compatible' => FALSE,
     );
-    $this->assertEquals($library['license'], $expected_license, 'Expected license metadata found.');
+    $this->assertEquals($library['license'], $expected_license);
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Core/Asset/library_test_files/licenses.libraries.yml b/core/tests/Drupal/Tests/Core/Asset/library_test_files/licenses.libraries.yml
new file mode 100644
index 0000000..455b4c5
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Asset/library_test_files/licenses.libraries.yml
@@ -0,0 +1,72 @@
+# No license information: should default to GPL 2.0 or later..
+no-license-info:
+  version: 1.0
+  js:
+    no-license-info.js: {}
+  css:
+    base:
+      no-license-info.css: {}
+
+# A library with all assets licensed under the GPL-compatible GPL 2 license.
+gpl2:
+  version: 1.0
+  license:
+    name: gpl2
+    url: https://url-to-gpl2-license
+    gpl-compatible: true
+  js:
+    gpl2.js: {}
+  css:
+    base:
+      gpl2.css: {}
+
+# A library with all assets licensed under the GPL-compatible MIT license.
+mit:
+  version: 1.0
+  license:
+    name: MIT
+    url: https://url-to-mit-license
+    gpl-compatible: true
+  js:
+    mit.js: {}
+  css:
+    base:
+      mit.css: {}
+
+# A library with all assets licensed under the GPL-compatible Public Domain.
+public-domain:
+  version: 1.0
+  license:
+    name: Public Domain
+    url: https://url-to-public-domain-license
+    gpl-compatible: true
+  js:
+    public-domain.js: {}
+  css:
+    base:
+      public-domain.css: {}
+
+# A library with all assets licensed under the GPL-incompatible Apache license.
+apache:
+  version: 1.0
+  license:
+    name: apache
+    url: https://url-to-apache-license
+    gpl-compatible: false
+  js:
+    apache.js: {}
+  css:
+    base:
+      apache.css: {}
+
+# A library with all assets licensed under the GPL-incompatible copyright.
+copyright:
+  version: 1.0
+  license:
+    name: © Some company
+    gpl-compatible: false
+  js:
+    copyright.js: {}
+  css:
+    base:
+      copyright.css: {}
diff --git a/core/tests/Drupal/Tests/Core/Asset/library_test_files/licenses_missing_information.libraries.yml b/core/tests/Drupal/Tests/Core/Asset/library_test_files/licenses_missing_information.libraries.yml
new file mode 100644
index 0000000..f36d061
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Asset/library_test_files/licenses_missing_information.libraries.yml
@@ -0,0 +1,9 @@
+# No license information for a 3rd party library (it has the 'remote' key).
+no-license-info-but-remote:
+  version: 1.0
+  remote: https://url-to-remote
+  js:
+    no-license-info-but-remote.js: {}
+  css:
+    base:
+      no-license-info-but-remote.css: {}