Symfony 5.3.0-RC1 has just been released. Here is a list of the most
important changes:

security #cve-2021-21424 [SecurityCore] Fix user enumeration via response body on invalid credentials (@chalasr)
bug #41275 Fixes Undefined method call (@faizanakram99)
feature #41175 [Security] [RememberMe] Add support for parallel requests doing remember-me re-authentication (@Seldaek)
bug #41269 [SecurityBundle] Remove invalid unused service (@chalasr)
feature #41247 [Security] Deprecate the old authentication mechanisms (@chalasr)
bug #41139 [Security] [DataCollector] Remove allows anonymous information in datacollector (@ismail1432)
bug #41254 [SecurityHttp] Fix handling secure: auto using the new RememberMeAuthenticator (@chalasr)
bug #41230 [FrameworkBundle][Validator] Fix deprecations from Doctrine Annotations+Cache (@derrabus)
bug #41206 [Mailer] Fix SES API call with UTF-8 Addresses (@jderusse)
bug #41240 Fixed deprecation warnings about passing null as parameter (@derrabus)
bug #41241 [Finder] Fix gitignore regex build with “” (@mvorisek)
bug #41224 [HttpClient] fix adding query string to relative URLs with scoped clients (@nicolas-grekas)
bug #41233 [DependencyInjection][ProxyManagerBridge] Don’t call clas _exists() on null (@derrabus)
bug #41214 [Console] fix registering command aliases when using the new “cmd|alias” syntax for names (@nicolas-grekas)
bug #41211 [Notifier] Add missing charset to content-type for Slack notifier (@norkunas)
bug #41210 [Console] Fix Windows code page support (@orkan)

Want to upgrade to this new release? Because Symfony protects
backwards-compatibility very closely, this should be quite easy. Use
SymfonyInsight upgrade reports
to detect the code you will need to change in your project and
read our upgrade
documentation to learn more.

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