Symfony News

New in Symfony 5.1: Access decision based on voter priority

Contributed by
Andreas Schempp
in #34548.

In Symfony applications, security voters centralize the authorization logic which decides if a given user can access to the requested resource. They are regular Symfony services tagged with the security.voter tag, so they can define their priorities via the priority attribute of the tag.

In practice this voter priority is mostly irrelevant, because of the access decision strategies used by Symfony:

• affirmative, grants access as soon as there is one voter granting access;
• consensus, grants access if there are more voters granting access than denying;
• unanimous, grants access if there is no voter denying access.

That's why in Symfony 5.1 we've added a new access decision strategy called priority which grants or denies access depending on the first voter that does not abstain. In this case, the voter priority is essential, because the first non-abstain decision will be the final decision:

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# config/packages/security.yaml
security:
    access_decision_manager:
        strategy: priority
        # ...

This feature originated from the Contao CMS project, which is built with Symfony, and defines some default permissions which other extensions/bundles must be able to override. This new priority access decision strategy is the only one able to do that.