Version 4 supported
This version of Silverstripe CMS is still supported though will not receive any additional features. Go to documentation for the most recent stable version.

Built-in middleware

Silverstripe CMS has a number of Middleware components. You may find them in the SilverStripe\Control\Middleware namespace.

AllowedHostsMiddlewareSecures requests by only allowing a whitelist of Host values
CanonicalURLMiddlewareURL normalisation and redirection
ChangeDetectionMiddlewareChange detection via Etag / IfModifiedSince headers, conditionally sending a 304 not modified if possible.
ConfirmationMiddlewareChecks whether user manual confirmation is required for HTTPRequest
ExecMetricMiddlewareDisplay execution metrics in DEV mode
FlushMiddlewareTriggers a call to flush() on all Flushable implementors
HTTPCacheControlMiddlewareControls HTTP response cache headers
RateLimitMiddlewareAccess throttling, controls HTTP Retry-After header
SessionMiddlewarePHP Session initialisation
TrustedProxyMiddlewareRewrites headers that provide IP and host details from upstream proxies
URLSpecialsMiddlewareControls some of the URL special variables