Crow/docs/guides/CORS.md

Crow Allows a developer to set CORS policies by using the CORSHandler middleware.

This middleware can be added to the app simply by defining a #!cpp crow::App<crow::CORSHandler>. This will use the default CORS rules globally

The CORS rules can be modified by first getting the middleware via #!cpp auto& cors = app.get_middleware<crow::CORSHandler>();. The rules can be set per URL prefix using prefix(), per blueprint using blueprint(), or globally via global(). These will return a CORSRules object which contains the actual rules for the prefix, blueprint, or application. For more details go here.

CORSRules can be modified using the methods origin(), methods(), headers(), max_age(), allow_credentials(), or ignore(). For more details on these methods and what default values they take go here.