Draft: Resolve #2923419 "Method to use 2.x"

Closes #2923419

src/Plugin/OpenIDConnectClientBase.php

@@ -191,6 +191,58 @@ abstract class OpenIDConnectClientBase extends PluginBase implements OpenIDConne
     }
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function refreshTokens(string $refresh_token): ?array {
+    // Exchange a refresh token for new tokens.
+    $endpoints = $this->getEndpoints();
+
+    $request_options = [
+      'form_params' => [
+        'refresh_token' => $refresh_token,
+        'client_id' => $this->configuration['client_id'],
+        'client_secret' => $this->configuration['client_secret'],
+        'grant_type' => 'refresh_token',
+      ],
+      'headers' => [
+        'Accept' => 'application/json',
+      ],
+    ];
+    if ($scopes = implode(' ', $this->getClientScopes())) {
+      $request_options['form_params']['scope'] = $scopes;
+    }
+
+    /* @var \GuzzleHttp\ClientInterface $client */
+    $client = $this->httpClient;
+    try {
+      $response = $client->post($endpoints['token'], $request_options);
+      $response_data = json_decode((string) $response->getBody(), TRUE);
+
+      // Expected result.
+      $tokens = [
+        'id_token' => isset($response_data['id_token']) ? $response_data['id_token'] : NULL,
+        'access_token' => isset($response_data['access_token']) ? $response_data['access_token'] : NULL,
+      ];
+      if (array_key_exists('expires_in', $response_data)) {
+        $tokens['expire'] = REQUEST_TIME + $response_data['expires_in'];
+      }
+      if (array_key_exists('refresh_token', $response_data)) {
+        $tokens['refresh_token'] = $response_data['refresh_token'];
+      }
+      return $tokens;
+    }
+    catch (Exception $e) {
+      $variables = [
+        '@message' => 'Could not refresh tokens',
+        '@error_message' => $e->getMessage(),
+      ];
+      $this->loggerFactory->get('openid_connect_' . $this->pluginId)
+        ->error('@message. Details: @error_message', $variables);
+      return FALSE;
+    }
+  }
+
   /**
    * {@inheritdoc}
    */