405 method options not allowed in asp.net web api controller? - asp.net

Question

I have this very common issue where it says method not allowed (OPTIONS) for a GET request. I am getting the following error whenever I make an API call. I have this setting in web.config:
<system.webServer>
<modules>
<remove name="WebDAVModule"/>
</modules>
<httpProtocol>
<customHeaders>
<add name="Access-Control-Allow-Origin" value="*"/>
<add name="Access-Control-Allow-Headers" value="Origin, Authorization, X-Requested-With, Content-Type, Accept"/>
<add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE, OPTIONS"/>
</customHeaders>
</httpProtocol>
<handlers>
<remove name="WebDAV"/>
<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>
I tried using Asp.Net.WebApi.Cors and enforcing CORS globally using EnableCors() for all origin headers and methods and that did not work either.

Answer 1

In your handlers after <remove name="OPTIONSVerbHandler"/>, add this:
<add name="OPTIONSVerbHandler" path="*" verb="OPTIONS"
modules="IsapiModule" requireAccess="None"
scriptProcessor="C:\Windows\System32\inetsrv\asp.dll"
resourceType="Unspecified" />
See the answer at IIS hijacks CORS Preflight OPTIONS request.
Or maybe even just this:
<add name="OPTIONSVerbHandler" path="*" verb="OPTIONS"
modules="ProtocolSupportModule" requireAccess="None" />
If that doesn’t work, something that will is adding the following in your global.asax or other code:
protected void Application_BeginRequest(object sender,EventArgs e)
{
HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*");
if(HttpContext.Current.Request.HttpMethod == "OPTIONS")
{
HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE");
HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "Content-Type, Accept");
HttpContext.Current.Response.AddHeader("Access-Control-Max-Age", "1728000" );
HttpContext.Current.Response.End();
}
}