CORS WebAPI 2
app.UseCors(CorsOptions.AllowAll)
One thing that caught me out after enabling the middleware is that IIS was intercepting pre-flight requests. To ensure ASP.NET handles OPTION requests, add the following in web.config:
<system.webServer>
<handlers>
<remove name="ExtensionlessUrlHandler-Integrated-4.0" />
<remove name="OPTIONSVerbHandler" />
<remove name="TRACEVerbHandler" />
<add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
</handlers>
</system.webServer>