Invoking a custom Apex REST Web service method always uses system context. Consequently, the
current user's credentials are not used, and any user who has access to these methods can use
their full power, regardless of permissions, field-level security, or sharing rules. Developers
who expose methods using the Apex REST annotations should therefore take care that they are not
inadvertently exposing any sensitive data.
Apex class methods that are exposed through the Apex REST API don't enforce
object permissions and field-level security by default. We recommend that you make use of the
appropriate object or field describe result methods to check the current user’s access
level on the objects and fields that the Apex REST API method is accessing. See DescribeSObjectResult Class and DescribeFieldResult Class.
Also,
sharing rules (record-level access) are enforced only when declaring a class with the with sharing keyword. This requirement applies to all Apex
classes, including to classes that are exposed through Apex REST API. To enforce sharing rules
for Apex REST API methods, declare the class that contains these methods with the with sharing keyword. See Using the with sharing or without sharing Keywords.
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